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132-633: The Janiculum is one of the best locations in Rome for a scenic view of central Rome with its domes and bell towers . Other sights on the Janiculum include the church of San Pietro in Montorio , on what was formerly thought to be the site of St Peter 's crucifixion ; a small shrine known as the Tempietto, designed by Donato Bramante , marks the supposed site of Peter's death. The Janiculum also houses

264-586: A Baroque fountain built by Pope Paul V in the late 17th century, the Fontana dell'Acqua Paola , and several foreign research institutions, including the American and Spanish Academies in Rome . The Hill is also the location of The American University of Rome , Pontifical Urban University , and Pontifical North American College , as well as the Orto Botanico dell'Università di Roma "La Sapienza" and

396-455: A forge , fulling stocks in a fulling mill and so on. However, in corn mills rotation about a vertical axis was required to drive its stones. The horizontal rotation was converted into the vertical rotation by means of gearing, which also enabled the runner stones to turn faster than the waterwheel. The usual arrangement in British and American corn mills has been for the waterwheel to turn

528-405: A gear mechanism, and the other equipped with a horizontal waterwheel without such a mechanism. The former type can be further subdivided, depending on where the water hits the wheel paddles, into undershot, overshot, breastshot and pitchback (backshot or reverse shot) waterwheel mills. Another way to classify water mills is by an essential trait about their location: tide mills use the movement of

660-400: A " whispering gallery " at its base that at certain places transmits distinct sound to other distant places in the gallery. The half-domes over the apses of Byzantine churches helped to project the chants of the clergy. Although this can complement music, it may make speech less intelligible, leading Francesco Giorgi in 1535 to recommend vaulted ceilings for the choir areas of a church, but

792-480: A central point. The validity of this is unclear, as domes built underground with corbelled stone layers are in compression from the surrounding earth. The precise definition of "pendentive" has also been a source of academic contention, such as whether or not corbelling is permitted under the definition and whether or not the lower portions of a sail vault should be considered pendentives. Domes with pendentives can be divided into two kinds: simple and compound . In

924-713: A circle . Because they reduce the portion of the dome in tension, these domes are strong but have increased radial thrust. Many of the largest existing domes are of this shape. Masonry saucer domes, because they exist entirely in compression, can be built much thinner than other dome shapes without becoming unstable. The trade-off between the proportionately increased horizontal thrust at their abutments and their decreased weight and quantity of materials may make them more economical, but they are more vulnerable to damage from movement in their supports. Also called gadrooned , fluted , organ-piped , pumpkin , melon , ribbed , parachute , scalloped , or lobed domes, these are

1056-554: A circular base alone, circular or polygonal base, circular, elliptical, or polygonal base, or an undefined area. Definitions specifying vertical sections include: semicircular, pointed, or bulbous; semicircular, segmental or pointed; semicircular, segmental, pointed, or bulbous; semicircular, segmental, elliptical, or bulbous; and high profile, hemispherical, or flattened. Sometimes called "false" domes, corbel domes achieve their shape by extending each horizontal layer of stones inward slightly farther than

1188-516: A circular base for a drum or compound dome, smoothly continue their curvature to form the dome itself. The dome gives the impression of a square sail pinned down at each corner and billowing upward. These can also be thought of as saucer domes upon pendentives. Sail domes are based upon the shape of a hemisphere and are not to be confused with elliptic parabolic vaults, which appear similar but have different characteristics. In addition to semicircular sail vaults there are variations in geometry such as

1320-437: A dam on the river above the mill and a more elaborate millpond, sluice gate, mill race and spillway or tailrace. An inherent problem in the overshot mill is that it reverses the rotation of the wheel. If a miller wishes to convert a breastshot mill to an overshot wheel all the machinery in the mill has to be rebuilt to take account of the change in rotation. An alternative solution was the pitchback or backshot wheel. A launder

1452-745: A day. By 610 or 670 AD, the watermill was introduced to Japan via Korean Peninsula . It also became known in Tibet by at least 641 AD. According to Greek historical tradition, India received water-mills from the Roman Empire in the early 4th century AD when a certain Metrodoros introduced "water-mills and baths, unknown among them [the Brahmans] till then". Engineers under the Caliphates adopted watermill technology from former provinces of

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1584-429: A dome. The top of a dome is the "crown". The inner side of a dome is called the "intrados" and the outer side is called the "extrados". As with arches, the "springing" of a dome is the base level from which the dome rises and the "haunch" is the part that lies roughly halfway between the base and the top. Domes can be supported by an elliptical or circular wall called a "drum". If this structure extends to ground level,

1716-546: A flat ceiling filled with as many coffers as possible for where preaching would occur. Cavities in the form of jars built into the inner surface of a dome may serve to compensate for this interference by diffusing sound in all directions, eliminating echoes while creating a "divine effect in the atmosphere of worship." This technique was written about by Vitruvius in his Ten Books on Architecture , which describes bronze and earthenware resonators. The material, shape, contents, and placement of these cavity resonators determine

1848-402: A hemispherical dome can be 2.5 times thinner than a semicircular arch, and a dome with the profile of an equilateral arch can be thinner still. The optimal shape for a masonry dome of equal thickness provides for perfect compression, with none of the tension or bending forces against which masonry is weak. For a particular material, the optimal dome geometry is called the funicular surface ,

1980-452: A horizontal shaft on which is also mounted a large pit wheel . This meshes with the wallower , mounted on a vertical shaft, which turns the (larger) great spur wheel (mounted on the same shaft). This large face wheel , set with pegs, in turn, turned a smaller wheel (such as a lantern gear ) known as a stone nut, which was attached to the shaft that drove the runner stone. The number of runner stones that could be turned depended directly upon

2112-427: A horizontal water wheel on a vertical axle, and the other with a vertical wheel on a horizontal axle. The oldest of these were horizontal mills in which the force of the water, striking a simple paddle wheel set horizontally in line with the flow turned a runner stone balanced on the rynd which is atop a shaft leading directly up from the wheel. The bedstone does not turn. The problem with this type of mill arose from

2244-516: A limited number of simple elements and joints and efficiently resolve a dome's internal forces. Their efficiency is said to increase with size. Although not first invented by Buckminster Fuller , they are associated with him because he designed many geodesic domes and patented them in the United States. The hemispherical dome is a surface formed by the rotation around a vertical axis of a semicircle . Like other "rotational domes" formed by

2376-517: A low rise to span ratio or covering a rectangular plan. Sail vaults of all types have a variety of thrust conditions along their borders, which can cause problems, but have been widely used from at least the sixteenth century. The second floor of the Llotja de la Seda is covered by a series of nine meter wide sail vaults. Also called segmental domes (a term sometimes also used for cloister vaults), or calottes , these have profiles of less than half

2508-495: A military defense of the short-lived Roman Republic in late April 1849. The hill also features a number of statues and monuments of prominent Italians . A 2011 guide published by the local Associazione Amilcare Cipriani group, after an extensive restoration of these monuments, lists a total of 84 busts on the hill. 41°53′30″N 12°27′40″E  /  41.89167°N 12.46111°E  / 41.89167; 12.46111 Domes A dome (from Latin domus )

2640-608: A mostly rural work process, than the ancient urban-centered literary class had been. By Carolingian times, references to watermills had become "innumerable" in Frankish records. The Domesday Book , compiled in 1086, records 5,624 watermills in England alone. Later research estimates a less conservative number of 6,082 that should be considered a minimum as the northern reaches of England were never properly recorded. In 1300, this number had risen to between 10,000 and 15,000. By

2772-521: A pointed and bulbous tradition inherited by some early Islamic mosques. Modern academic study of the topic has been controversial and confused by inconsistent definitions, such as those for cloister vaults and domical vaults. Dictionary definitions of the term "dome" are often general and imprecise. Generally-speaking, it "is non-specific, a blanket-word to describe an hemispherical or similar spanning element." Published definitions include: hemispherical roofs alone; revolved arches ; and vaults on

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2904-553: A powerful mortar. The aggregate transitioned over the centuries to pieces of fired clay, then to Roman bricks. By the sixth century, bricks with large amounts of mortar were the principle vaulting materials. Pozzolana appears to have only been used in central Italy. Brick domes were the favored choice for large-space monumental coverings until the Industrial Age , due to their convenience and dependability. Ties and chains of iron or wood could be used to resist stresses. In

3036-463: A shaft with a horizontal axis to one with a vertical axis. Although to date only a few dozen Roman mills are archaeologically traced, the widespread use of aqueducts in the period suggests that many remain to be discovered. Recent excavations in Roman London, for example, have uncovered what appears to be a tide mill together with a possible sequence of mills worked by an aqueduct running along

3168-611: A short drum, as can be seen at the Shah Cheragh (1852–1853), first appeared in the Qajar period . Domes have remained important in modern mausoleums, and domed cisterns and icehouses remain common sights in the countryside. Water mill A watermill or water mill is a mill that uses hydropower . It is a structure that uses a water wheel or water turbine to drive a mechanical process such as milling (grinding) , rolling , or hammering . Such processes are needed in

3300-450: A single arch or a set of multiple projecting nested arches placed diagonally over an internal corner. Squinch forms also include trumpet arches, niche heads (or half-domes), trumpet arches with "anteposed" arches, and muqarnas arches. Squinches transfer the weight of a dome across the gaps created by the corners and into the walls. Pendentives are triangular sections of a sphere, like concave spandrels between arches, and transition from

3432-564: A single point of origin. Their appearance in northern Russian architecture predates the Tatar occupation of Russia and so is not easily explained as the result of that influence. They became popular in the second half of the 15th century in the Low Countries of Northern Europe, possibly inspired by the finials of minarets in Egypt and Syria, and developed in the 16th and 17th centuries in

3564-420: A single waterwheel driving more than one set of stones was drawn by Henry Beighton in 1723 and published in 1744 by J. T. Desaguliers . The overshot wheel was a later innovation in waterwheels and was around two and a half times more efficient than the undershot. The undershot wheel, in which the main water wheel is simply set into the flow of the mill race, suffers from an inherent inefficiency stemming from

3696-588: A smaller diameter dome immediately above them, as in the Hagia Sophia, or a drum and dome, as in many Renaissance and post-Renaissance domes, with both forms resulting in greater height. One of the earliest types of ribbed vault, the first known examples are found in the Great Mosque of Córdoba in the 10th century. Rather than meeting in the center of the dome, the ribs characteristically intersect one another off-center, forming an empty polygonal space in

3828-477: A source of water, used to provide additional power to watermills and water-raising machines. Fulling mills, and steel mills may have spread from Al-Andalus to Christian Spain in the 12th century. Industrial watermills were also employed in large factory complexes built in al-Andalus between the 11th and 13th centuries. The engineers of the Islamic world used several solutions to achieve the maximum output from

3960-567: A system of squinches or pendentives used to accommodate the transition in shape from a rectangular or square space to the round or polygonal base of the dome. The dome's apex may be closed or may be open in the form of an oculus , which may itself be covered with a roof lantern and cupola. Domes have a long architectural lineage that extends back into prehistory . Domes were built in ancient Mesopotamia , and they have been found in Persian , Hellenistic , Roman , and Chinese architecture in

4092-543: A type of dome divided at the base into curved segments, which follow the curve of the elevation . "Fluted" may refer specifically to this pattern as an external feature, such as was common in Mamluk Egypt . The "ribs" of a dome are the radial lines of masonry that extend from the crown down to the springing. The central dome of the Hagia Sophia uses the ribbed method, which accommodates a ring of windows between

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4224-542: A vertical axis of a semi-ellipse . Like other "rotational domes" formed by the rotation of a curve around a vertical axis, ellipsoidal domes have circular bases and horizontal sections and are a type of "circular dome" for that reason. Geodesic domes are the upper portion of geodesic spheres. They are composed of a framework of triangles in a polyhedron pattern. The structures are named for geodesics and are based upon geometric shapes such as icosahedrons , octahedrons or tetrahedrons . Such domes can be created using

4356-408: A vertical-waterwheel via a gear mechanism, and the other equipped with a horizontal-waterwheel without such a mechanism. The former type can be further divided, depending on where the water hits the wheel paddles, into undershot, overshot, breastshot and reverse shot waterwheel mills. The Greeks invented the two main components of watermills, the waterwheel and toothed gearing, and used, along with

4488-581: A water-powered grain-mill to have existed near the palace of king Mithradates VI Eupator at Cabira , Asia Minor , before 71 BC. The Roman engineer Vitruvius has the first technical description of a watermill, dated to 40/10 BC; the device is fitted with an undershot wheel and power is transmitted via a gearing mechanism . He also seems to indicate the existence of water-powered kneading machines. The Greek epigrammatist Antipater of Thessalonica tells of an advanced overshot wheel mill around 20 BC/10 AD. He praised for its use in grinding grain and

4620-499: A watermill. One solution was to mount them to piers of bridges to take advantage of the increased flow. Another solution was the ship mill, a type of watermill powered by water wheels mounted on the sides of ships moored in midstream . This technique was employed along the Tigris and Euphrates rivers in 10th-century Iraq , where large ship mills made of teak and iron could produce 10 tons of flour from corn every day for

4752-399: Is an architectural element similar to the hollow upper half of a sphere . There is significant overlap with the term cupola , which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a matter of controversy and there are a wide variety of forms and specialized terms to describe them. A dome can rest directly upon a rotunda wall, a drum , or

4884-776: Is called a Melon dome. A paraboloid dome is a surface formed by the rotation around a vertical axis of a sector of a parabola. Like other "rotational domes" formed by the rotation of a curve around a vertical axis, paraboloid domes have circular bases and horizontal sections and are a type of "circular dome" for that reason. Because of their shape, paraboloid domes experience only compression, both radially and horizontally. Also called sail vaults , handkerchief vaults , domical vaults (a term sometimes also applied to cloister vaults), pendentive domes (a term that has also been applied to compound domes), Bohemian vaults , or Byzantine domes , this type can be thought of as pendentives that, rather than merely touching each other to form

5016-803: Is carried out in the UK at Daniels Mill , Little Salkeld Mill and Redbournbury Mill . This was boosted to overcome flour shortages during the Covid pandemic. Some old mills are being upgraded with modern hydropower technology, such as those worked on by the South Somerset Hydropower Group in the UK. In some developing countries, watermills are still widely used for processing grain. For example, there are thought to be 25,000 operating in Nepal, and 200,000 in India. Many of these are still of

5148-401: Is made a complete and self-supporting ring. The upper portion of a masonry dome is always in compression and is supported laterally, so it does not collapse except as a whole unit and a range of deviations from the ideal in this shallow upper cap are equally stable. Because voussoir domes have lateral support, they can be made much thinner than corresponding arches of the same span. For example,

5280-481: Is not well documented. That the dome was known to early Mesopotamia may explain the existence of domes in both China and the West in the first millennium BC. Another explanation, however, is that the use of the dome shape in construction did not have a single point of origin and was common in virtually all cultures long before domes were constructed with enduring materials. Corbelled stone domes have been found from

5412-546: Is the igloo , a shelter built from blocks of compact snow and used by the Inuit , among others. The Himba people of Namibia construct "desert igloos" of wattle and daub for use as temporary shelters at seasonal cattle camps, and as permanent homes by the poor. Extraordinarily thin domes of sun-baked clay 20 feet in diameter, 30 feet high, and nearly parabolic in curve, are known from Cameroon . The historical development from structures like these to more sophisticated domes

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5544-428: Is the tide mill . This mill might be of any kind, undershot, overshot or horizontal but it does not employ a river for its power source. Instead a mole or causeway is built across the mouth of a small bay. At low tide, gates in the mole are opened allowing the bay to fill with the incoming tide. At high tide the gates are closed, trapping the water inside. At a certain point a sluice gate in the mole can be opened allowing

5676-517: Is the first to have squinches create a regular octagon as a base for the dome, which then became the standard practice. Cylindrical or polygonal plan tower tombs with conical roofs over domes also exist beginning in the 11th century. The Seljuk Empire 's notables built tomb-towers, called "Turkish Triangles", as well as cube mausoleums covered with a variety of dome forms. Seljuk domes included conical, semi-circular, and pointed shapes in one or two shells. Shallow semi-circular domes are mainly found from

5808-625: Is the name of an ancient town founded by the god Janus (the two-faced god of beginnings). In Book VIII of the Aeneid by Virgil (Publius Vergilius Maro), King Evander shows Aeneas (the Trojan hero of this epic poem) the ruins of Saturnia and Janiculum on the Capitoline Hill near the Arcadian city of Pallanteum (the future site of Rome) (see line 54, Bk. 8). Virgil uses these ruins to stress

5940-502: Is the preeminent role of France in the introduction of new innovative uses of waterpower. However, he has drawn attention to the dearth of studies of the subject in several other countries. The waterwheel was found in China from 30 AD onwards, when it was used to power trip hammers , the bellows in smelting iron , and in one case, to mechanically rotate an armillary sphere for astronomical observation (see Zhang Heng ). Although

6072-474: The Aurelian walls in the late 3rd century. A breastshot wheel mill dating to the late 2nd century AD was excavated at Les Martres-de-Veyre , France. The 3rd century AD Hierapolis water-powered stone sawmill is the earliest known machine to incorporate the mechanism of a crank and connecting rod . Further sawmills, also powered by crank and connecting rod mechanisms, are archaeologically attested for

6204-534: The Byzantine Empire , having been applied for centuries in those provinces prior to the Muslim conquests , including modern-day Syria , Jordan , Israel , Algeria , Tunisia , Morocco , and Spain (see List of ancient watermills ). The industrial uses of watermills in the Islamic world date back to the 7th century, while horizontal-wheeled and vertical-wheeled watermills were both in widespread use by

6336-490: The Middle East and Central Asia , domes and drums constructed from mud brick and baked brick were sometimes covered with brittle ceramic tiles on the exterior to protect against rain and snow. The new building materials of the 19th century and a better understanding of the forces within structures from the 20th century opened up new possibilities. Iron and steel beams, steel cables, and pre-stressed concrete eliminated

6468-647: The Neolithic period in the ancient Near East , and in the Middle East to Western Europe from antiquity. The kings of Achaemenid Persia held audiences and festivals in domical tents derived from the nomadic traditions of central Asia. Simple domical mausoleums existed in the Hellenistic period. The remains of a large domed circular hall in the Parthian capital city of Nyssa has been dated to perhaps

6600-473: The Roman Empire . So-called 'Greek Mills' used water wheels with a horizontal wheel (and vertical shaft). A "Roman Mill" features a vertical wheel (on a horizontal shaft). Greek style mills are the older and simpler of the two designs, but only operate well with high water velocities and with small diameter millstones. Roman style mills are more complicated as they require gears to transmit the power from

6732-597: The Romans , undershot, overshot and breastshot waterwheel mills. The earliest evidence of a water-driven wheel appears in the technical treatises Pneumatica and Parasceuastica of the Greek engineer Philo of Byzantium (ca. 280−220 BC). The British historian of technology M.J.T. Lewis has shown that those portions of Philo of Byzantium's mechanical treatise which describe water wheels and which have been previously regarded as later Arabic interpolations, actually date back to

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6864-522: The Safavid dynasty (1501–1732) are characterized by a distinctive bulbous profile and are considered the last generation of Persian domes. They are generally thinner than earlier domes and are decorated with a variety of colored glazed tiles and complex vegetal patterns, and they were influential on those of other Islamic styles, such as the Mughal architecture of India. An exaggerated style of onion dome on

6996-548: The Sui dynasty (581–618 AD) was said to operate hundreds of them by the beginning of the 6th century. A source written in 612 AD mentions Buddhist monks arguing over the revenues gained from watermills. The Tang dynasty (618–907 AD) 'Ordinances of the Department of Waterways' written in 737 AD stated that watermills should not interrupt riverine transport and in some cases were restricted to use in certain seasons of

7128-476: The University of Kassel in 1983. A masonry dome produces thrusts downward and outward. They are thought of in terms of two kinds of forces at right angles from one another: meridional forces (like the meridians , or lines of longitude, on a globe) are compressive only, and increase towards the base, while hoop forces (like the lines of latitude on a globe) are in compression at the top and tension at

7260-512: The ancient world ". It featured 16 overshot waterwheels to power an equal number of flour mills. The capacity of the mills has been estimated at 4.5 tons of flour per day, sufficient to supply enough bread for the 12,500 inhabitants occupying the town of Arelate at that time. A similar mill complex existed on the Janiculum hill, whose supply of flour for Rome 's population was judged by emperor Aurelian important enough to be included in

7392-565: The ancient world , as well as among a number of indigenous building traditions throughout the world. Dome structures were common in both Byzantine architecture and Sasanian architecture , which influenced that of the rest of Europe and Islam , respectively, in the Middle Ages . The domes of European Renaissance architecture spread from Italy in the early modern period , while domes were frequently employed in Ottoman architecture at

7524-632: The granary in Baghdad . More than 300 watermills were at work in Iran till 1960. Now only a few are still working. One of the famous ones is the water mill of Askzar and the water mill of the Yazd city, still producing flour. Typically, water is diverted from a river or impoundment or mill pond to a turbine or water wheel, along a channel or pipe (variously known as a flume , head race, mill race , leat , leet, lade (Scots) or penstock ). The force of

7656-404: The 20th century have allowed for large dome-shaped structures that deviate from the traditional compressive structural behavior of masonry domes. Popular usage of the term has expanded to mean "almost any long-span roofing system". The word " cupola " is another word for "dome", and is usually used for a small dome upon a roof or turret . "Cupola" has also been used to describe the inner side of

7788-547: The 6th century AD water-powered stone sawmills at Gerasa and Ephesus . Literary references to water-powered marble saws in what is now Germany can be found in Ausonius 4th century AD poem Mosella . They also seem to be indicated about the same time by the Christian saint Gregory of Nyssa from Anatolia , demonstrating a diversified use of water-power in many parts of the Roman Empire . The earliest turbine mill

7920-555: The 9th century. A variety of industrial watermills were used in the Islamic world, including gristmills , hullers , sawmills , ship mills, stamp mills , steel mills , sugar mills , and tide mills . By the 11th century, every province throughout the Islamic world had these industrial watermills in operation, from al-Andalus and North Africa to the Middle East and Central Asia . Muslim and Middle Eastern Christian engineers also used crankshafts and water turbines , gears in watermills and water-raising machines , and dams as

8052-532: The Aqua Traiana, turned to run parallel to the aqueduct for some distance, and then turned back to feed into the aqueduct again. It appeared that the northern mill race had 3 or 4 millwheels of 2.30 m diameter and width about 1.65 m to provide a sufficiently large working area, but only 2.6 m between their axle centres, which must have reduced efficiency due to turbulence between them. The southern race had one larger wheel. The site resembles Barbegal , although

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8184-461: The British chemist and sinologist Joseph Needham speculates that the water-powered millstone could have existed in Han China by the 1st century AD, there is no sufficient literary evidence for it until the 5th century AD. In 488 AD, the mathematician and engineer Zu Chongzhi had a watermill erected which was inspected by Emperor Wu of Southern Qi (r. 482–493 AD). The engineer Yang Su of

8316-535: The Commune of Rome to resume the tradition after a twenty-year interruption. The hill is featured in the third section of Ottorino Respighi 's tone poem Pines of Rome . The crest of the Janiculum is dominated by the 1895 equestrian Monument to Garibaldi , designed by Italian sculptor Emilio Gallori . This site was chosen for its proximity to the Villa Doria Pamphili , where Garibaldi mounted

8448-539: The Greek 3rd century BC original. The sakia gear is, already fully developed, for the first time attested in a 2nd-century BC Hellenistic wall painting in Ptolemaic Egypt . Lewis assigns the date of the invention of the horizontal-wheeled mill to the Greek colony of Byzantium in the first half of the 3rd century BC, and that of the vertical-wheeled mill to Ptolemaic Alexandria around 240 BC. The Greek geographer Strabo reports in his Geography

8580-608: The Italian word duomo , the German/Icelandic/Danish word dom ("cathedral"), and the English word dome as late as 1656, when it meant a "Town-House, Guild-Hall, State-House, and Meeting-House in a city." The French word dosme came to acquire the meaning of a cupola vault, specifically, by 1660. This French definition gradually became the standard usage of the English dome in the eighteenth century as many of

8712-649: The Netherlands before spreading to Germany, becoming a popular element of the baroque architecture of Central Europe. German bulbous domes were also influenced by Russian and Eastern European domes. The examples found in various European architectural styles are typically wooden. Examples include Kazan Church in Kolomenskoye and the Brighton Pavilion by John Nash . In Islamic architecture, they are typically made of masonry, rather than timber, with

8844-582: The Palazzo Montorio, residence of the Ambassadors of Spain. The Villa Lante al Gianicolo by Giulio Romano (1520–21) is an important early building by the Mannerist master, also with magnificent views. The Janiculum was a center for the cult of the god Janus : its position overlooking the city made it a good place for augurs to observe the auspices . In Roman mythology, Janiculum

8976-532: The Seljuk era. The double-shell domes were either discontinuous or continuous. The domed enclosure of the Jameh Mosque of Isfahan , built in 1086-7 by Nizam al-Mulk , was the largest masonry dome in the Islamic world at that time, had eight ribs, and introduced a new form of corner squinch with two quarter domes supporting a short barrel vault. In 1088 Tāj-al-Molk, a rival of Nizam al-Mulk, built another dome at

9108-424: The base, with the transition in a hemispherical dome occurring at an angle of 51.8 degrees from the top. The thrusts generated by a dome are directly proportional to the weight of its materials. Grounded hemispherical domes generate significant horizontal thrusts at their haunches. The outward thrusts in the lower portion of a hemispherical masonry dome can be counteracted with the use of chains incorporated around

9240-416: The buckets fill, the weight of the water starts to turn the wheel. The water spills out of the bucket on the down side into a spillway leading back to river. Since the wheel itself is set above the spillway, the water never impedes the speed of the wheel. The impulse of the water on the wheel is also harnessed in addition to the weight of the water once in the buckets. Overshot wheels require the construction of

9372-570: The case of the simple dome , the pendentives are part of the same sphere as the dome itself; however, such domes are rare. In the case of the more common compound dome , the pendentives are part of the surface of a larger sphere below that of the dome itself and form a circular base for either the dome or a drum section. The fields of engineering and architecture have lacked common language for domes, with engineering focused on structural behavior and architecture focused on form and symbolism. Additionally, new materials and structural systems in

9504-467: The center. Geometry is a key element of the designs, with the octagon being perhaps the most popular shape used. Whether the arches are structural or purely decorative remains a matter of debate. The type may have an eastern origin, although the issue is also unsettled. Examples are found in Spain, North Africa, Armenia, Iran, France, and Italy. The ellipsoidal dome is a surface formed by the rotation around

9636-519: The church of Santo Tomás de las Ollas in Spain has an oval dome over its oval plan. Other examples of medieval oval domes can be found covering rectangular bays in churches. Oval plan churches became a type in the Renaissance and popular in the Baroque style. The dome built for the basilica of Vicoforte by Francesco Gallo was one of the largest and most complex ever made. Although the ellipse

9768-505: The circle being considered the most perfect of forms. According to E. Baldwin Smith, from the late Stone Age the dome-shaped tomb was used as a reproduction of the ancestral, god-given shelter made permanent as a venerated home of the dead. The instinctive desire to do this resulted in widespread domical mortuary traditions across the ancient world, from the stupas of India to the tholos tombs of Iberia . By Hellenistic and Roman times,

9900-459: The circumference or with external buttressing, although cracking along the meridians is natural. For small or tall domes with less horizontal thrust, the thickness of the supporting arches or walls can be enough to resist deformation, which is why drums tend to be much thicker than the domes they support. Unlike voussoir arches, which require support for each element until the keystone is in place, domes are stable during construction as each level

10032-456: The comparable shape in three dimensions to a catenary curve for a two-dimensional arch. Adding a weight to the top of a pointed dome, such as the heavy cupola at the top of Florence Cathedral , changes the optimal shape to more closely match the actual pointed shape of the dome. The pointed profiles of many Gothic domes more closely approximate the optimal dome shape than do hemispheres, which were favored by Roman and Byzantine architects due to

10164-400: The corners of a square bay to the circular base of a dome. The curvature of the pendentives is that of a sphere with a diameter equal to the diagonal of the square bay. Pendentives concentrate the weight of a dome into the corners of the bay. The earliest domes in the Middle East were built with mud-brick and, eventually, with baked brick and stone. Domes of wood allowed for wide spans due to

10296-454: The date of the earliest tide mills, all of which were discovered on the Irish coast: A 6th century vertical-wheeled tide mill was located at Killoteran near Waterford . A twin flume horizontal-wheeled tide mill dating to c. 630 was excavated on Little Island . Alongside it, another tide mill was found which was powered by a vertical undershot wheel. The Nendrum Monastery mill from 787

10428-443: The dome's surface of revolution, or be straight lengths with the connecting points or nodes lying upon the surface of revolution. Single-layer structures are called frame or skeleton types and double-layer structures are truss types, which are used for large spans. When the covering also forms part of the structural system, it is called a stressed skin type. The formed surface type consists of sheets joined at bent edges to form

10560-553: The domical tholos had become the customary cemetery symbol. Domes and tent-canopies were also associated with the heavens in Ancient Persia and the Hellenistic-Roman world. A dome over a square base reflected the geometric symbolism of those shapes. The circle represented perfection, eternity, and the heavens. The square represented the earth. An octagon was intermediate between the two. The distinct symbolism of

10692-600: The draining water to drive a mill wheel or wheels. This is particularly effective in places where the tidal differential is very great, such as the Bay of Fundy in Canada where the tides can rise fifty feet, or the now derelict village of Tide Mills, East Sussex . The last two examples in the United Kingdom which are restored to working conditions can be visited at Eling , Hampshire and at Woodbridge , Suffolk . Run of

10824-458: The early 7th century, watermills were also well established in Ireland . A century later they began to spread across the former Roman Rhine and Danube frontier into the other parts of Germany . Ship mills and tide mills , both of which yet unattested for the ancient period, were introduced in the 6th century. In recent years, a number of new archaeological finds has consecutively pushed back

10956-492: The earth, we taste again the golden age . The Roman encyclopedist Pliny mentions in his Naturalis Historia of around 70 AD water-powered trip hammers operating in the greater part of Italy. There is evidence of a fulling mill in 73/74 AD in Antioch , Roman Syria . The 2nd century AD multiple mill complex of Barbegal in southern France has been described as "the greatest known concentration of mechanical power in

11088-483: The effect they have: reinforcing certain frequencies or absorbing them. Also called a corbelled dome , cribbed dome , or false dome , these are different from a 'true dome' in that they consist of purely horizontal layers. As the layers get higher, each is slightly cantilevered , or corbeled , toward the center until meeting at the top. A monumental example is the Mycenaean Treasury of Atreus from

11220-542: The excavations show that they were undershot rather than overshot in design (i. e. with the stream entering at the bottom of the wheel, not the top). The mills were still in use in 537, when the Goths besieging the city cut off their water supply, the Aqua Traiana . They were later restored and may have remained in operation until at least the time of Pope Gregory IV (827–844). The Aurelian Walls were continued up

11352-421: The fact that the wheel itself, entering the water behind the main thrust of the flow driving the wheel, followed by the lift of the wheel out of the water ahead of the main thrust, actually impedes its own operation. The overshot wheel solves this problem by bringing the water flow to the top of the wheel. The water fills buckets built into the wheel, rather than the simple paddle wheel design of undershot wheels. As

11484-567: The fallen in the wars of Italian independence are on the Janiculum. Daily at noon, a cannon fires once from the Janiculum in the direction of the Tiber as a time signal. This tradition goes back to December 1847, when the cannon of the Castel Sant'Angelo gave the sign to the surrounding belltowers to start ringing at midday. In 1904, the ritual was transferred to the Janiculum and continued until 1939. On 21 April 1959, popular appeal convinced

11616-472: The first century AD, showing "...the existence of a monumental domical tradition in Central Asia that had hitherto been unknown and which seems to have preceded Roman Imperial monuments or at least to have grown independently from them." It likely had a wooden dome. Persian architecture likely inherited an architectural tradition of dome-building dating back to the earliest Mesopotamian domes. Due to

11748-952: The first century BC, such as the Tabularium of Rome from 78 BC. Others include the Baths of Antoninus in Carthage (145–160) and the Palatine Chapel at Aachen (13th – 14th century). The most famous example is the Renaissance octagonal dome of Filippo Brunelleschi over the Florence Cathedral. Thomas Jefferson , the third president of the United States, installed an octagonal dome above the West front of his plantation house, Monticello . Also called domes on pendentives or pendentive domes (a term also applied to sail vaults), compound domes have pendentives that support

11880-632: The first examples in Asia Minor date to around 4000 B.C. The geometry was eventually defined using combinations of circular arcs, transitioning at points of tangency. If the Romans created oval domes, it was only in exceptional circumstances. The Roman foundations of the oval plan Church of St. Gereon in Cologne point to a possible example. Domes in the Middle Ages also tended to be circular, though

12012-457: The forces of Lars Porsena occupied the Janiculum and laid siege to Rome. During the third century AD, a complex of water-mills was built here to grind grain to provide bread flour for the city. As revealed by excavations in the 1990s under the present American Academy in Rome, they sat astride the aqueduct Aqua Traiana and were in brick-faced concrete with a cocciopesto floor. In the limited excavated area, two mill races branched obliquely off

12144-574: The forefront of Persian architecture as a result. Pre-Islamic domes in Persia are commonly semi-elliptical, with pointed domes and those with conical outer shells being the majority of the domes in the Islamic periods. The area of north-eastern Iran was, along with Egypt, one of two areas notable for early developments in Islamic domed mausoleums, which appear in the tenth century. The Samanid Mausoleum in Transoxiana dates to no later than 943 and

12276-451: The heavenly or cosmic tent stemming from the royal audience tents of Achaemenid and Indian rulers was adopted by Roman rulers in imitation of Alexander the Great , becoming the imperial baldachin . This probably began with Nero , whose " Golden House " also made the dome a feature of palace architecture. The dual sepulchral and heavenly symbolism was adopted by early Christians in both

12408-479: The hill by the emperor Aurelian (reigned AD 270–275) to include the water mills . The mills were already known from observations by R. Lanciani in the 1880s. The Janiculum is the site of a battle in 1849 between the forces of Garibaldi , defending the revolutionary Roman Republic against French forces, who were fighting to restore the temporal power of the Pope over Rome. Several monuments to Garibaldi and to

12540-467: The lack of gearing; the speed of the water directly set the maximum speed of the runner stone which, in turn, set the rate of milling. Most watermills in Britain and the United States of America had a vertical waterwheel, one of four kinds: undershot, breast-shot, overshot and pitchback wheels. This vertical produced rotary motion around a horizontal axis, which could be used (with cams) to lift hammers in

12672-482: The late Bronze Age . A single or double layer space frame in the form of a dome, a braced dome is a generic term that includes ribbed , Schwedler , three-way grid , lamella or Kiewitt , lattice , and geodesic domes . The different terms reflect different arrangements in the surface members. Braced domes often have a very low weight and are usually used to cover spans of up to 150 meters. Often prefabricated, their component members can either lie on

12804-411: The lower one until they meet at the top. A "false" dome may also refer to a wooden dome. The Italian use of the term finto , meaning "false", can be traced back to the 17th century in the use of vaulting made of reed mats and gypsum mortar. "True" domes are said to be those whose structure is in a state of compression, with constituent elements of wedge-shaped voussoirs , the joints of which align with

12936-403: The modern world can be found over religious buildings, legislative chambers, sports stadiums, and a variety of functional structures. The English word "dome" ultimately derives from the ancient Greek and Latin domus ("house"), which, up through the Renaissance, labeled a revered house, such as a Domus Dei , or "House of God", regardless of the shape of its roof. This is reflected in the uses of

13068-660: The most impressive Houses of God were built with monumental domes, and in response to the scientific need for more technical terms. Across the ancient world, curved-roof structures that would today be called domes had a number of different names reflecting a variety of shapes, traditions, and symbolic associations. The shapes were derived from traditions of pre-historic shelters made from various impermanent pliable materials and were only later reproduced as vaulting in more durable materials. The hemispherical shape often associated with domes today derives from Greek geometry and Roman standardization, but other shapes persisted, including

13200-449: The need for external buttressing and enabled much thinner domes. Whereas earlier masonry domes may have had a radius to thickness ratio of 50, the ratio for modern domes can be in excess of 800. The lighter weight of these domes not only permitted far greater spans, but also allowed for the creation of large movable domes over modern sports stadiums. Experimental rammed earth domes were made as part of work on sustainable architecture at

13332-691: The opposite end of the same mosque with interlacing ribs forming five-pointed stars and pentagons. This is considered the landmark Seljuk dome, and may have inspired subsequent patterning and the domes of the Il-Khanate period. The use of tile and of plain or painted plaster to decorate dome interiors, rather than brick, increased under the Seljuks. Beginning in the Ilkhanate , Persian domes achieved their final configuration of structural supports, zone of transition, drum, and shells, and subsequent evolution

13464-581: The place of a prince during royal ceremonies. Over time such domes became primarily focal points for decoration or the direction of prayer. The use of domes in mausoleums can likewise reflect royal patronage or be seen as representing the honor and prestige that domes symbolized, rather than having any specific funerary meaning. The wide variety of dome forms in medieval Islam reflected dynastic, religious, and social differences as much as practical building considerations. Because domes are concave from below, they can reflect sound and create echoes. A dome may have

13596-627: The power available for British grain milling. By the early 20th century, availability of cheap electrical energy made the watermill obsolete in developed countries although some smaller rural mills continued to operate commercially later throughout the century. A few historic mills such as the Water Mill , Newlin Mill and Yates Mill in the US and The Darley Mill Centre in the UK still operate for demonstration purposes. Small-scale commercial production

13728-608: The power from a toothed annular ring that is mounted near the outer edge of the wheel. This drives the machinery using a spur gear mounted on a shaft rather than taking power from the central axle . However, the basic mode of operation remains the same; gravity drives machinery through the motion of flowing water . Toward the end of the 19th century, the invention of the Pelton wheel encouraged some mill owners to replace over- and undershot wheels with Pelton wheel turbines driven through penstocks . A different type of watermill

13860-419: The production of many material goods, including flour , lumber , paper , textiles , and many metal products. These watermills may comprise gristmills , sawmills , paper mills , textile mills , hammermills , trip hammering mills, rolling mills , and wire drawing mills. One major way to classify watermills is by wheel orientation (vertical or horizontal), one powered by a vertical waterwheel through

13992-465: The reduction of human labour: Hold back your hand from the mill, you grinding girls; even if the cockcrow heralds the dawn, sleep on. For Demeter has imposed the labours of your hands on the nymphs , who leaping down upon the topmost part of the wheel, rotate its axle; with encircling cogs, it turns the hollow weight of the Nisyrian millstones . If we learn to feast toil-free on the fruits of

14124-458: The relatively light and flexible nature of the material and were the normal method for domed churches by the 7th century, although most domes were built with the other less flexible materials. Wooden domes were protected from the weather by roofing, such as copper or lead sheeting. Domes of cut stone were more expensive and never as large, and timber was used for large spans where brick was unavailable. Roman concrete used an aggregate of stone with

14256-417: The ribs at the base of the dome. The central dome of St. Peter's Basilica also uses this method. Cultures from pre-history to modern times constructed domed dwellings using local materials. Although it is not known when the first dome was created, sporadic examples of early domed structures have been discovered. The earliest discovered may be four small dwellings made of Mammoth tusks and bones. The first

14388-448: The river schemes do not divert water at all and usually involve undershot wheels the mills are mostly on the banks of sizeable rivers or fast flowing streams. Other watermills were set beneath large bridges where the flow of water between the stanchions was faster. At one point London bridge had so many water wheels beneath it that bargemen complained that passage through the bridge was impaired. In 1870 watermills still produced 2/3 of

14520-471: The rotation of a curve around a vertical axis, hemispherical domes have circular bases and horizontal sections and are a type of "circular dome" for that reason. They experience vertical compression along their meridians, but horizontally experience compression only in the portion above 51.8 degrees from the top. Below this point, hemispherical domes experience tension horizontally, and usually require buttressing to counteract it. According to E. Baldwin Smith, it

14652-402: The round building may be called a " rotunda ". Drums are also called " tholobates " and may or may not contain windows. A " tambour " or " lantern " is the equivalent structure over a dome's oculus, supporting a cupola. When the base of the dome does not match the plan of the supporting walls beneath it (for example, a dome's circular base over a square bay ), techniques are employed to bridge

14784-456: The same time. Baroque and Neoclassical architecture took inspiration from Roman domes. Advancements in mathematics, materials, and production techniques resulted in new dome types. Domes have been constructed over the centuries from mud, snow, stone, wood, brick, concrete, metal, glass, and plastic. The symbolism associated with domes includes mortuary , celestial , and governmental traditions that have likewise altered over time. The domes of

14916-495: The scarcity of wood in many areas of the Iranian plateau and Greater Iran , domes were an important part of vernacular architecture throughout Persian history. The Persian invention of the squinch , a series of concentric arches forming a half-cone over the corner of a room, enabled the transition from the walls of a square chamber to an octagonal base for a dome in a way reliable enough for large constructions and domes moved to

15048-633: The side of the River Fleet . In 537 AD, ship mills were ingeniously used by the East Roman general Belisarius , when the besieging Goths cut off the water supply for those mills. These floating mills had a wheel that was attached to a boat moored in a fast flowing river. The surviving evidence for watermills sharply increases with the emergence of documentary genres such as monastic charters , Christian hagiography and Germanic legal codes . These were more inclined to address watermilling,

15180-454: The significance of the Capitoline Hill as the religious center of Rome. According to Livy , the Janiculum was incorporated into ancient Rome during the time of king Ancus Marcius to prevent an enemy from occupying it. It was fortified by a wall, and a bridge was built across the Tiber to join it to the rest of the city. During the war between Rome and Clusium in 508 BC, it is said that

15312-465: The structure. Also called domical vaults (a term sometimes also applied to sail vaults), polygonal domes , coved domes , gored domes , segmental domes (a term sometimes also used for saucer domes), paneled vaults , or pavilion vaults , these are domes that maintain a polygonal shape in their horizontal cross section. The component curved surfaces of these vaults are called severies , webs , or cells . The earliest known examples date to

15444-406: The supply of water available. As waterwheel technology improved mills became more efficient, and by the 19th century, it was common for the great spur wheel to drive several stone nuts, so that a single water wheel could drive as many as four stones. Each step in the process increased the gear ratio which increased the maximum speed of the runner stone. Adjusting the sluice gate and thus the flow of

15576-457: The thick and heavy bulging portion serving to buttress against the tendency of masonry domes to spread at their bases. The Taj Mahal is a famous example. An oval dome is a dome of oval shape in plan, profile, or both. The term comes from the Latin ovum , meaning "egg". The earliest oval domes were used by convenience in corbelled stone huts as rounded but geometrically undefined coverings, and

15708-573: The tide; ship mills are water mills onboard (and constituting) a ship. Watermills impact the river dynamics of the watercourses where they are installed. During the time watermills operate channels tend to sedimentate , particularly backwater . Also in the backwater area, inundation events and sedimentation of adjacent floodplains increase. Over time however these effects are cancelled by river banks becoming higher. Where mills have been removed, river incision increases and channels deepen. There are two basic types of watermills, one powered by

15840-556: The two shells of the dome have significantly different profiles, which spread rapidly throughout the region. The development of taller drums also continued into the Timurid period. The large, bulbous, fluted domes on tall drums that are characteristic of 15th century Timurid architecture were the culmination of the Central Asian and Iranian tradition of tall domes with glazed tile coverings in blue and other colors. The domes of

15972-505: The two. One technique is to use corbelling, progressively projecting horizontal layers from the top of the supporting wall to the base of the dome, such as the corbelled triangles often used in Seljuk and Ottoman architecture. The simplest technique is to use diagonal lintels across the corners of the walls to create an octagonal base. Another is to use arches to span the corners, which can support more weight. A variety of these techniques use what are called " squinches ". A squinch can be

16104-426: The use of domes in architecture and in the ciborium , a domical canopy like the baldachin used as a ritual covering for relics or the church altar . The celestial symbolism of the dome, however, was the preeminent one by the Christian era . In the early centuries of Islam, domes were closely associated with royalty. A dome built in front of the mihrab of a mosque, for example, was at least initially meant to emphasize

16236-486: The water past the main wheel allowed the miller to compensate for seasonal variations in the water supply. Finer speed adjustment was made during the milling process by tentering , that is, adjusting the gap between the stones according to the water flow, the type of grain being milled, and the grade of flour required. In many mills (including the earliest) the great spur wheel turned only one stone, but there might be several mills under one roof. The earliest illustration of

16368-596: The water's movement drives the blades of a wheel or turbine, which in turn rotates an axle that drives the mill's other machinery. Water leaving the wheel or turbine is drained through a tail race, but this channel may also be the head race of yet another wheel, turbine or mill. The passage of water is controlled by sluice gates that allow maintenance and some measure of flood control; large mill complexes may have dozens of sluices controlling complicated interconnected races that feed multiple buildings and industrial processes. Watermills can be divided into two kinds, one with

16500-456: The year. From other Tang-era sources of the 8th century, it is known that these ordinances were taken very seriously, as the government demolished many watermills owned by great families, merchants, and Buddhist abbeys that failed to acknowledge ordinances or meet government regulations. A eunuch serving Emperor Xuanzong of Tang (r. 712–756 AD) owned a watermill by 748 AD which employed five waterwheels that ground 300 bushels of wheat

16632-525: Was a shape likely known to the Assyrians, defined by Greek theoretical mathematicians, and standardized by Roman builders. Bulbous domes bulge out beyond their base diameters, offering a profile greater than a hemisphere. An onion dome is a greater than hemispherical dome with a pointed top in an ogee profile. They are found in the Near East , Middle East , Persia, and India and may not have had

16764-584: Was found by a farmer in Mezhirich , Ukraine, in 1965 while he was digging in his cellar and archaeologists unearthed three more. They date from 19,280 – 11,700 BC. In modern times , the creation of relatively simple dome-like structures has been documented among various indigenous peoples around the world. The wigwam was made by Native Americans using arched branches or poles covered with grass or hides. The Efé people of central Africa construct similar structures , using leaves as shingles. Another example

16896-561: Was found in Chemtou and Testour , Roman North Africa , dating to the late 3rd or early 4th century AD. A possible water-powered furnace has been identified at Marseille , France. Mills were commonly used for grinding grain into flour (attested by Pliny the Elder ), but industrial uses as fulling and sawing marble were also applied. The Romans used both fixed and floating water wheels and introduced water power to other provinces of

17028-522: Was known, in practice, domes of this shape were created by combining segments of circles. Popular in the 16th and 17th centuries, oval and elliptical plan domes can vary their dimensions in three axes or two axes. A sub-type with the long axis having a semicircular section is called a Murcia dome, as in the Chapel of the Junterones at Murcia Cathedral . When the short axis has a semicircular section, it

17160-436: Was placed at the end of the flume on the headrace, this turned the direction of the water without much loss of energy, and the direction of rotation was maintained. Daniels Mill near Bewdley , Worcestershire is an example of a flour mill that originally used a breastshot wheel, but was converted to use a pitchback wheel. Today it operates as a breastshot mill. Larger water wheels (usually overshot steel wheels) transmit

17292-405: Was restricted to variations in form and shell geometry. Characteristic of these domes are the use of high drums and several types of discontinuous double-shells, and the development of triple-shells and internal stiffeners occurred at this time. The construction of tomb towers decreased. The 7.5 meter wide double dome of Soltan Bakht Agha Mausoleum (1351–1352) is the earliest known example in which

17424-637: Was situated on an island in Strangford Lough in Northern Ireland . Its millstones are 830 mm in diameter and the horizontal wheel is estimated to have developed 7 ⁄ 8 horsepower (650 W) at its peak. Remains of an earlier mill dated at 619 were also found at the site. In a 2005 survey the scholar Adam Lucas identified the following first appearances of various industrial mill types in Western Europe. Noticeable

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