The early domes of the Middle Ages, particularly in those areas recently under Byzantine control, were an extension of earlier Roman architecture. The domed church architecture of Italy from the sixth to the eighth centuries followed that of the Byzantine provinces and, although this influence diminishes under Charlemagne, it continued on in Venice, Southern Italy, and Sicily. Charlemagne’s Palatine Chapel is a notable exception, being influenced by Byzantine models from Ravenna and Constantinople. The Dome of the Rock, an Umayyad Muslim religious shrine built in Jerusalem, was designed similarly to nearby Byzantine martyria and Christian churches. Domes were also built as part of Muslim palaces, throne halls, pavilions, and baths, and blended elements of both Byzantine and Persian architecture, using both pendentives and squinches. The origin of the crossed-arch dome type is debated, but the earliest known example is from the tenth century at the Great Mosque of Córdoba. In Egypt, a “keel” shaped dome profile was characteristic of Fatimid architecture. The use of squinches became widespread in the Islamic world by the tenth and eleventh centuries. Bulbous domes were used to cover large buildings in Syria after the eleventh century, following an architectural revival there, and the present shape of the Dome of the Rock’s dome likely dates from this time.
High Middle Ages
The schism between the churches of Constantinople and Rome was reflected in architecture. The Greek cross and domes of Byzantine architecture were found in areas of Byzantine cultural influence.
In Venice, the second and current St. Mark’s Basilica was built on the site of the first between 1063 and 1072, replacing the earlier church while replicating its Greek cross plan. Five domes vault the interior (one each over the four arms of the cross and one in the center). These domes were built in the Byzantine style, in imitation of the now lost Church of the Holy Apostles in Constantinople. Mounted over pendentives, each dome has a ring of windows at its base. These five windowed domes reflect the addition of windows (within tall drums) in the remodeled Byzantine original. However, the tall outer shells at St. Mark’s were not added until after 1204. The later high wooden outer domes with lead roofing and cupolas were added to St. Mark’s Basilica between 1210 and 1270, allowing the church to be seen from a great distance. In addition to allowing for a more imposing exterior, building two distinct shells in a dome improved weather protection. It was a rare practice before the 11th century. The fluted and onion-shaped cupolas of the domes may have been added in the mid-fifteenth century to complement the ogee arches added to the facade in the late Gothic period. Their shape may have been influenced by the open and domed wooden pavilions of Persia or by other eastern models. Initially, only the center dome had one.
Domes in Romanesque architecture are generally found within crossing towers at the intersection of a church’s nave and transept, which conceal the domes externally. Called a tiburio, this tower-like structure often has a blind arcade near the roof. Romanesque domes are typically octagonal in plan and use corner squinches to translate a square bay into a suitable octagonal base. Octagonal cloister vaults appear “in connection with basilicas almost throughout Europe” between 1050 and 1100. The precise form differs from region to region. They were popular in medieval Italy, in brick.
Holy Roman Empire
The architecture of the areas of northern Italy that were a part of the Holy Roman Empire developed differently from the rest of the Italian peninsula. The earliest use of the octagonal cloister vault within an external housing at the crossing of a cruciform church may be at Acqui Cathedral in Acqui Terme, Italy, which was completed in 1067. This became increasingly popular as a Romanesque feature over the course of the next fifty years. The first Lombard church to have a lantern tower, concealing an octagonal cloister vault, was San Nazaro in Milan, just after 1075. Many other churches followed suit in the late 11th and early 12th centuries, such as the Basilica of San Michele Maggiore in Pavia and the Basilica of Sant’Ambrogio in Milan. At Sant’Ambrogio, the original plan for the church did not include a domed crossing and it was modified to include one, as also happened with the first plan at Pisa and at Speyer.
Pisa Cathedral, built between 1063 and 1118, includes a high elliptical dome at the crossing of its nave and transept. The marble dome was one of the first in Romanesque architecture and is considered the masterpiece of Romanesque domes. Rising 48 meters above a rectangular bay, the shape of the dome was unique at the time. The rectangular bay’s dimensions are 18 meters by 13.5 meters. Squinches were used at the corners to create an elongated octagon in a system similar to that of the contemporary Basilica of San Lorenzo in Milan and corbelling was used to create an oval base for the dome. The tambour on which the dome rests dates to between 1090 and 1100, and it is likely that the dome itself was built at that time. There is evidence that the builders did not originally plan for the dome and decided on the novel shape to accommodate the rectangular crossing bay, which would have made an octagonal cloister vault very difficult. Additionally, the dome may have originally been covered by an octagonal lantern tower that was removed in the 1300s, exposing the dome, to reduce weight on foundations not designed to support it. This would have been done no later than 1383, when the Gothic loggetta on the exterior of the dome was added, along with the buttressing arches on which it rests.
An aspiring competitor to Pisa, the city of Florence took the opposite side in the conflict between Pope and Emperor, siding with the Pope in Rome. This was reflected architecturally in the “proto-renaissance” style of its buildings. The eight-sided Florence Baptistery, with its large octagonal cloister vault beneath a pyramidal roof, was likely built between 1059 and 1128, with the dome and attic built between 1090 and 1128. The lantern above the dome is dated to 1150. It takes inspiration from the Pantheon in Rome for its oculus and much of its interior decoration, although the pointed dome is structurally similar to Lombard domes, such as that of the later Cremona Baptistery. The domes of Pisa Cathedral and Florence Baptistery may be the two earliest domes in Tuscany and were the two largest until about 1150.
In southern Italy, the Basilica of San Sabino in Canosa di Puglia was built around 1080 with five domes over its “T-shaped layout”, with three domes across the transept and another two out over the nave. Its cruciform plan, use of domes, and the later addition of an external mausoleum suggest that it may have been a Norman analog to the Byzantine Church of the Holy Apostles. It appears to have inspired a series of churches in Apulia with domed naves. The date of construction has been challenged as being decades too late. The multi-domed churches of Cyprus have been proposed as the inspiration for the basilica’s domes and for the three-domed naves of later churches in the region, which date mostly from the period of Norman rule, but this is also a topic of debate. San Benedetto at Conversano, the Ognissanti of Valenzano, San Francesco at Trani, and the Cathedral of San Corrado at Molfetta were built in the 11th to 13th centuries with pendentive domes. San Corrado also incorporates “squinch-like niches” between the pendentives and drums of two of its three domes.
In France, the 11th and 12th century Cathedral of Le Puy uses an unusual row of six octagonal domes on squinches over its nave, with the domes at the western end being at least a century later than those at the east end. A seventh dome is located in the normal position for a Romanesque dome on squinches: over the crossing. Other examples of this use over naves are rare and scattered. One is the large church of Saint Hilaire at Poitiers, which seems to have been influenced by Le Puy Cathedral. In 1130, its wide nave was narrowed with additional piers to form suitable square bays, which were vaulted with octagonal domes whose corner sides over trumpet squinches were so narrow that the domes resemble square cloister vaults with beveled corners. The earliest existing large French dome is believed to be the pendentive dome built by 1075 over the crossing of the Collegiate Church of St-Martin at Angers. It reportedly incorporates “pottery” in its structure, a technique used in the late Roman period.
The Crusades and Reconquista
The Crusades, beginning in 1095, also appear to have influenced domed architecture in Western Europe, particularly in the areas around the Mediterranean Sea. The Mausoleum of Bohemond (c. 1111-18), a Norman leader of the First Crusade, was built next to the Basilica of San Sabino in the southern Italian province of Apulia and has a hemispherical dome in a Byzantine style over a square building with a Greek cross plan.
Influence of the Church of the Holy Sepulchre
The Church of the Holy Sepulchre in Jerusalem seems to have had a wooden dome in two shells up to the 12th century, with some interruptions. After their establishing control of the city, the crusaders added a choir with a dome next to the existing rotunda. The French Romanesque addition replaced the eastern apse of the rotunda and a courtyard marking the center of the world and was consecrated on July 15, 1149, the fiftieth anniversary of the capture of the city. The new dome’s diameter of 10.4 meters was half that of the rotunda and it rested on four pointed arches on four pillars. It served as the coronation site for the crusader kings of Jerusalem.
The rotunda itself was covered by a conical structure from the 12th to the early 19th century. Pisa Baptistry was built in 1153 with a truncated cone in clear imitation of the Holy Sepulchre; an outer dome shell was added in the 14th century. The domed baptisteries of Cremona (1176) and Parma (1196) also appear to have been influenced by the rotunda. The 12th century rotunda of the Holy Sepulchre at Santo Stefano, Bologna, and the basilica at Neuvy-Saint-Sépulchre are imitations of Jerusalem’s Church of the Holy Sepulchre although, like many of the imitations across Europe, they differ in their details, including their domes.
In the Aquitaine region of southwest France, there are a large number of unusual domed Romanesque churches; over 250 in the Périgord region alone. The area is far from ports with regular contact with the East and the source of influence is not entirely settled. A study in 1976 of Romanesque churches in the south of France documented 130 with oval plan domes, such as the domes on pendentives at Saint-Martin-de-Gurson, Dordogne and Balzac, Charente. The oval shape appears to have been a practical solution to rectangular crossing bays. The use of pendentives to support domes in the Aquitaine region, rather than the squinches more typical of western medieval architecture, strongly implies a Byzantine influence.
Between the Garonne and Loire rivers there are known to have been at least seventy-seven churches whose naves were covered by a line of domes. Half of them are in the Périgord region. Most date to the twelfth century and sixty of them survive today. That the domes in this area were arranged in linear series has suggested the contemporary architecture of Cyprus as the inspiration, which was located on a pilgrimage route to the Holy Land. Cyprus had developed its own style of domed basilica during its period of neutrality between Byzantine and Arab rulers, using three domes of roughly equal size in a line over the nave and very little lighting. There are indications of a connection between Aquitaine and Cyprus just after the First Crusade.
The earliest of these French churches may be Angoulême Cathedral, built from 1105 to 1128. Its long nave is covered by four stone domes on pendentives, springing from pointed arches, the last of which covers the crossing and is surmounted by a stone lantern. Cahors Cathedral (c. 1100–1119) covers its nave with two large domes in the same manner and influenced the later building at Souillac. The abbey church at Fontevrault served as a burial place for Plantagenet royalty, including Richard the Lionheart, and is one of the most impressive examples. The earlier domed crossing is preceded by a wider nave covered by four domes, which was begun in 1125. The pendentives are original, but the four nave domes are modern replacements from about 1910. The cathedral of S. Front at Périgueux was built c. 1125–1150 and derives its five-domed cruciform plan ultimately from the Church of the Holy Apostles in Constantinople.
The remains of a crossing tower on the French Church of Saint-Jean de Montierneuf from about 1140 suggest an origin for some Spanish domes in a Romanesque and transitional Gothic style. The architectural influences at work here have been much debated, with proposed origins ranging from Jerusalem, Islamic Spain, or the Limousin region in western France to a mixture of sources. During the Reconquista, the Kingdom of León in northern Spain built three churches famous for their domed crossing towers, called “cimborios”, as it acquired new territories. The Cathedral of Zamora, the Cathedral of Salamanca, and the collegiate church of Toro were built around the middle of the 12th century. All three buildings have stone umbrella domes with sixteen ribs over windowed drums of either one or two stories, springing from pendentives. All three also have four small round towers engaged externally to the drums of the domes on their diagonal sides. Perhaps the masterpiece of the series, the Salamanca crossing tower has two stories of windows in its drum. Its outer stone fish-scale roof lined with gothic crockets is a separate corbelled layer with only eight lobes, which applies weight to the haunches of the sixteen-sided inner dome.
The Christian domed basilicas built in Sicily after the Norman Conquest also incorporate distinctly Islamic architectural elements. They include hemispherical domes positioned directly in front of apses, similar to the common positioning in mosques of domes directly in front of mihrabs, and the domes use four squinches for support, as do the domes of Islamic North Africa and Egypt. In other cases, domes exhibit Byzantine influences with tall drums, engaged columns, and blind arcades. Examples at Palermo include the Palatine Chapel (1132–1143), La Martorana (c. 1140s), and Zisa, Palermo (12th century). The church of San Giovanni degli Eremiti has five domes in a T-shaped arrangement and the Church of San Cataldo has three domes on squinches, with both showing clearly Islamic influence.
North Africa, Syria, and Al-Jazira
The so-called shrine of Imam al-Dawr in the village of al-Dawr, Iraq, is the earliest known example of a muqarnas dome, although it is unlikely to have been the first of its type. The dome rests on an octagonal base created by four squinches over a square bay. Three levels of muqarnas rise over this and are capped by a small cupola. The muqarnas cells are very large and resemble small squinches themselves. It was finished by 1090 by the court of an Uqaylid vassal of the Abbasid Caliphate of Baghdad and, although there are no surviving examples from Baghdad at this time, the large number of muqarnas domes known to have existed there by the end of the Middle Ages suggests that it could have been the source of the type.
In Islamic North Africa, there are several early muqarnas domes dating from the twelfth century. The earliest may be an Almoravid restoration between 1135 and 1140 of a series of stucco muqarnas domes over the axial nave of the mosque of the Qarawiyyin in Fez. The existence of a near contemporary example from 1154 in the maristan of Nur al-din in Damascus, Syria, and the earlier example of a muqarnas dome in al-Dawr, Iraq, suggests that the style was imported from Baghdad.
Most of the examples of muqarnas domes are found in Iraq and the Jazira, dated from the middle of the twelfth century to the Mongol invasion. The use of stucco to form the muqarnas pattern, suspended by a wooden framework from the exterior vault, was the least common in Iraq, although it would be very popular in North Africa and Spain. Because it used two shells, however, windows were restricted to the bases of the domes. They were otherwise used frequently in this type. In Iraq, the most common form was a single shell of brick, with the reverse of the interior pattern visible on the exterior. The Damascus mausoleum of Nur al-Din (1172) and the shrine of Zumurrud Khatun in Baghdad are examples. A third type is found only in Mosul from the beginning of the thirteenth century. It has a brick pyramidal roof, usually covered in green glazed tiles. Of the five preserved examples, the finest is the shrine of Awn al-Din, which used tiny colored tiles to cover the muqarnas cells themselves and incorporates small muqarnas domes into the tiers of muqarnas supporting the large eight-sided star at the center. This design led to a further development at the shrine of Shaykh Abd al-Samad in Natanz, Iran.
The architecture of Syria and the Jazira includes the widest variety of forms in the medieval Islamic world, being influenced by the surviving architecture of Late Antiquity, contemporary Christian buildings, and Islamic architecture from the east. There are some muqarnas domes of the Iraqi type, but most domes are slightly pointed hemispheres on either muqarnas pendentives or double zones of squinches and made of masonry, rather than brick and plaster. The domes cover single bay structures or are just a part of larger constructions. Syrian mausoleums consist of a square stone chamber with a single entrance and a mihrab and a brick lobed dome with two rows of squinches. The dome at the Silvan Mosque, 13.5 meters wide and built from 1152-1157, has an unusual design similar to the dome added to the Friday Mosque of Isfahan in 1086-1087: once surrounded by roofless aisles on three sides, it may have been meant to be an independent structure. The congregational mosque at Kızıltepe, with its well integrated dome of about 10 meters, is the masterpiece of Artuqid architecture.
The largest preserved Ayyubid dome is that of the Matbakh al-‘Ajami in Aleppo, resting on muqarnas pendentives. It may have been the palace residence of the al-‘Ajami family. The mausoleum over the tomb of Iman Al-Shafi‘i (built in 1211) has a large wooden double dome (rebuilt in 1722) about 29 meters high and, with the tombs of al-Malik al-Silah and the so-called Tomb of the Abassid Caliphs, is one of three important Ayyubid tombs in Cairo dating from the first half of the 13th century. The domed mausoleum was built 35 years after the madrassa ordered by Saladin at the site in 1176-7, which were introduced in Egypt after 1171 to counter Shia Islam. The only madrassa from the period to partly survive is the 1242 construction by As-Salih Ayyub on the site of the Fatimid Eastern Palace. The 10 meter wide domed tomb at its northern end led to the series of funerary madrassas built in Cairo by the Mamluk Sultans.
Late Romanesque and early Gothic Europe
The use of domes declined in Western Europe with the rise of Gothic architecture. Gothic domes are uncommon due to the use of rib vaults over naves, and with church crossings usually focused instead by a tall steeple, but there are examples of small octagonal crossing domes in cathedrals as the style developed from the Romanesque. Spaces of circular or octagonal plan were sometimes covered with vaults of a “double chevet” style, similar to the chevet apse vaulting in Gothic cathedrals. The crossing of Saint Nicholas at Blois is an example. The domed “Decagon” nave of St. Gereon’s Basilica in Cologne, Germany, a ten-sided space in an oval shape, was built between 1219 and 1227 upon the remaining low walls of a 4th-century Roman mausoleum. The ribbed domical vault rises four stories and 34 meters above the floor, covering an oval area 23.5 meters long and 18.7 meters wide. It is unique among the twelve Romanesque churches of Cologne, and in European architecture in general, and may have been the largest dome built in this period in Western Europe until the completion of the dome of Florence Cathedral.
In Italy, the dome of Siena Cathedral had an exposed profile as early as 1224, and this feature was retained in its reconstruction around 1260. The dome has two shells and was completed in 1264. It is set over an irregular 17.7-metre-wide (58 ft) hexagon with squinches to form an irregular twelve-sided base. No large dome had ever before been built over a hexagonal crossing. The current lantern dates from the 17th century and the current outer dome is a 19th-century replacement. The Basilica of St. Anthony of Padua was built between 1231 and 1300, in the early period of Italian Gothic architecture, and features seven domes with a blend of Gothic and Byzantine elements. Similar to St Mark’s Basilica in Venice, its nave, transepts, crossing, and the intermediate bay before the choir are covered by domes on pendentives in the Byzantine style. Externally, the crossing dome is covered with a conical spire. The choir dome, which may be later than the others, is uniquely Gothic with ribs.
In England, a dome with a pyramidal roof and lantern at the Abbot’s kitchen of Glastonbury Abbey dates to the early 14th century. Similar vaulting was built over the kitchen of Newenham Abbey by 1338. Timber star vaults such as those over York Minster’s octagonal Chapter house (ca. 1286–1296) and the elongated octagon plan of Wells Cathedral’s Lady Chapel (ca. 1320–1340) imitated much heavier stone vaulting. The wooden vaulting over the crossing of Ely Cathedral was built after the original crossing tower collapsed in 1322. It was conceived by Alan of Walsingham and designed by master carpenter William Hurley. Eight hammer vaults extend from eight piers over the 22 meter wide octagonal crossing and meet at the base of a large octagonal lantern, which is covered by a star vault.
Late Middle Ages
Star-shaped domes are found at the Moorish palace of the Alhambra in Granada, Spain, which contains domed audience halls built to mirror the heavenly constellations. The Hall of the Abencerrajes (c. 1333–91) and the Hall of the two Sisters (c. 1333–54) are extraordinarily developed examples of muqarnas domes, taking the tradition of the squinch in Islamic architecture from a functional element in the zone of transition to a highly ornamental covering for the dome itself. The structural elements of these two domes are actually brick vaulting, but these are completely covered by the intricate mocárabe stalactites. The lacy and star-shaped crossing dome of Burgos Cathedral (1567) may have been inspired by these examples, in addition to that built over the cathedral’s octagonal Chapel of the Condestable (1482–94) in the Gothic style.
In the first half of the fourteenth century, stone blocks replaced bricks as the primary building material in the dome construction of Mamluk Egypt, with the brick domes being only 20 percent of those constructed around 1322. Over the course of 250 years, around 400 domes were built in Cairo to cover the tombs of Mamluk sultans and emirs. Although they kept roughly the same proportions, the shift from brick to stone is also associated with an increase in the average span and height of about 3 to 4 meters, and a decrease in the thickness of the domes. The stone domes are generally 8 to 10 meters in diameter and 7 to 11 meters high. The Mausoleum of Farag Ibn Barquq (1398–1411) is an exceptional case, with a dome 16 meters wide and 12.8 meters tall.
The stone domes are generally single shells except at the conical crown, where there is a gap between inner and outer layers filled with earth and rubble and which contains the bases of the metal spires. Double shelled domes are rare, but an example is that of Al-Sultanyya Madrasa from 1360. The domes were constructed in circular rings, with the sizes decreasing towards the top of the dome and, because of this, it is possible that elaborate centering may not have been needed. Collapsed remains of some domes has revealed a layer of brick beneath the external stone, which could have supported and aligned the heavier stone during construction. Although the earliest stone domes do not have them, horizontal connections between the ashlar stone blocks were introduced in the fourteenth century, such as those made of teak wood in a dovetail shape used in the Mausoleum of Farag Ibn Barquq. Dome profiles were varied, with “keel-shaped”, bulbous, ogee, stilted domes, and others being used. On the drum, angles were chamfered, or sometimes stepped, externally and triple windows used in a tri-lobed arrangement on the faces.
Decoration for these first stone domes was initially the same external ribbing as earlier brick domes, and such brick domes would continue to be built throughout the Mamluk period, but more elaborate patterns of carving were introduced through the beginning of the sixteenth century. Early stones domes were plastered externally when not cut precisely enough, but improvements in technique over time would make this unnecessary. Spiral ribs were developed in the 1370s and zigzag patterns were common both by the end of the fourteenth century and again at the end of the fifteenth century. In the fifteenth century, interlaced star and floral designs were used in a tiled pattern. The uniqueness of a pattern on a mausoleum dome helped to associate that dome with the individual buried there.
The twin-domes of the Sultaniyya complex (c. 1360) and the narrow dome of Yunus al-Dawadar (c. 1385) are unusual in that they have muqarnas at the base of their external ribs, a feature of ribbed domes in Persia. The first example of the zigzag pattern is on the dome of Mahmud al-Kurdi (1394–95), and at least fourteen subsequent domes also used it. The first example of a dome in Cairo with a star pattern is the mausoleum of al-Ashraf Barsbay. The dome of Qaytbay in Cairo’s northern cemetery combines geometric and arabesque patterns and is one of the finest. Internally, the squinches of the zone of transition developed into miniaturized and pointed versions that were used row upon row over the entire expanded zone and bordered above and below by plain surfaces. Bulbous cupolas on minarets were used in Egypt beginning around 1330, spreading to Syria in the following century.
Exposed domes were common in Tuscany and a source of regional distinctiveness by the 1380s. The exposed outer dome of Pisa Baptistery was built over its earlier inner conical roof in the 14th century. If an external lantern tower was also removed from Pisa Cathedral in the 1300s, exposing the dome, one reason may have been to stay current with more recent projects in the region, such as the domed cathedrals of Siena and Florence. Rapid progress on a radical expansion of Siena Cathedral, which would have involved replacing the existing dome with a larger one, was halted not long after the city was struck with an outbreak of the Black Death in 1348. Its dome was originally topped with a copper orb, similar to that over Pisa’s dome today, but this was replaced in 1385 by a cupola surmounted by a smaller sphere and cross.
It was only a few years after the city of Siena had decided to abandon the massive expansion and redesign of their cathedral in 1355 that Florence decided to greatly expand theirs. A plan for the dome of Florence Cathedral was settled by 1357. However, in 1367 it was proposed to alter the church plan at the east end to increase the scale of the octagonal dome, widening it from 62 to 72 braccia, with the intent to further surpass the domes of Pisa and Siena, and this modified plan was ratified in 1368, under Master of Works Francesco Talenti. The construction guilds of Florence had sworn to adhere to the model of the dome created in 1367, with a “quinto acuto” pointed profile, but the scale of this new dome was so ambitious that experts for the Opera del Duomo, the board supervising the construction, expressed the opinion as early as 1394 that the dome could not be accomplished. The enlarged dome would span the entire 42-metre (138 ft) width of the three aisled nave, just 2 meters less than that of the Roman Pantheon, the largest dome in the world. And because the distances between the angles of the octagon were even farther apart at 45.5 metres (149 ft), the average span of the dome would be marginally wider than that of the Pantheon. At 144 braccia, the height of the dome would evoke the holy number of the Heavenly Jerusalem mentioned in the Book of Revelation. By 1413, with the exception of one of the three apses, the east end of the church had been completed up to the windowed octagonal drum but the problem of building the huge dome did not yet have a solution. In 1417, the master builder in charge of the project retired and a competition for dome designs was begun in August 1418. Brunelleschi’s dome, designed in 1418, follows the height and curvature mandated in 1367.
Filippo Brunelleschi and Lorenzo Ghiberti were made joint leaders of the project to build the dome for Florence Cathedral in 1420. Brunelleschi’s plan to use suspended scaffolding for the workers won out over alternatives such as building a provisional stone support column in the center of the crossing or filling the space with earth. The octagonal brick domical vault was built between 1420 and 1436, with Ghiberti resigning in 1433. The lantern surmounting the dome, also designed by Brunelleschi, was not begun until 1446, after his death. It was completed by Michelozzo di Bartolommeo and Bernardo Rossellino in 1467. Brunelleschi had also planned for a two-story external gallery and cornice to be built at the top of the drum where a strip of unclad masonry can be seen today. Although a portion of it was constructed on the southeast side beginning in 1508, work stopped after the visual effect was criticized by Michelangelo.
The dome is 42 meters wide and made of two shells. A stairway winds between them. Eight white stone external ribs mark the edges of the eight sides, next to the red tile roofing, and extend from the base of the dome to the base of the cupola. Each of the eight sides of the dome also conceal a pair of intermediate stone ribs that are connected to the main ribs by means of a series of masonry rings. A temporary wooden tension ring still exists near the bottom of the dome. Three horizontal chains of sandstone blocks notched together and reinforced with lead-coated iron cramps also extend the entire circumference of the dome: one at the base (where radial struts from this chain protrude to the exterior), one a third of the way up the dome, and one two thirds of the way up the dome. Only four major cracks have been observed on the inner dome, compared to about fourteen each on the domes of the Pantheon and St. Peter’s Basilica.
Although the design of the dome is very different from that of the Pantheon and it is unclear what the influences were, it does share some similarities with earlier and smaller brick domes in Persia. The use of a herringbone pattern in the brick allowed for short horizontal sections of the layers of the dome to be completed as self-supporting units. Over 32 meters in height, it remains the largest masonry dome ever built. The dome can be described as a cloister vault, with the eight ribs at the angles concentrating weight on the supporting piers. The dome is not itself Renaissance in style, although the lantern is closer.
The Low Countries of northwest Europe
In the fifteenth century, pilgrimages to and flourishing trade relations with the Near East exposed the Low Countries of northwest Europe to the use of bulbous domes in the architecture of the Orient. Although the first expressions of their European use are in the backgrounds of paintings, architectural uses followed. The Dome of the Rock and its bulbous dome being so prominent in Jerusalem, such domes apparently became associated by visitors with the city itself. In Bruges, The Church of the Holy Cross, designed to symbolize the Holy Sepulchre, was finished with a Gothic church tower capped by a bulbous cupola on a hexagonal shaft in 1428. Sometime between 1466 and 1500, a tower added to the Chapel of the Precious Blood was covered by a bulbous cupola very similar to Syrian minarets. Likewise, in Ghent, an octagonal staircase tower for the Church of St. Martin d’Ackerghem, built in the beginning of the sixteenth century, has a bulbous cupola like a minaret. These cupolas were made of wood covered with copper, as were the examples over turrets and towers in the Netherlands at the end of the fifteenth century, many of which have been lost. The earliest example from the Netherlands that has survived is the bulbous cupola built in 1511 over the town hall of Middelburg. Multi-story spires with truncated bulbous cupolas supporting smaller cupolas or crowns became popular in the following decades.
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