Dome - History - Roman and Byzantine Domes

Roman and Byzantine Domes

Roman domes of the pagan period are essentially found in three environments: baths, villas and palaces, and tombs. Oculi are common features. The Romans also used semi-domes, half a dome "cut" vertically, in niches and the exedras of basilicas.

The octagonal Tower of the Winds in Athens, built by Antigonus of Cyrrhestus, has a flat, monolithic, stone dome. Varro's book on agriculture, written about the same time, describes an aviary with a wooden dome decorated with the eight winds which is compared by analogy to the eight winds depicted on the Tower of the Winds. This aviary with its wooden dome may represent a fully developed type. Wooden domes in general would have allowed for very wide spans. Their earlier use may have inspired the development and introduction of large stone domes of previously unprecedented size. Complex wooden forms were also necessary for centering and support, the construction of which seems to have eventually become more efficient and standardized.

Roman baths played a leading role in the development of domed construction in general, and monumental domes in particular. Modest domes in baths dating from the 2nd and 1st centuries BC are seen in Pompeii, in the frigidaria of the Terme Stabiane and the Terme del Foro. According to Vitruvius, the temperature and humidity of domed tepidaria could be regulated by raising or lowering bronze discs located under the oculus. Domes were particularly well suited to the hot rooms of baths circular in plan to facilitate even heating from the walls. However, the extensive use of domes did not occur before the 1st century AD.

The first known large Roman dome is the so-called "Temple of Mercury" in Baiae, a concrete bath hall dating from the age of Augustus (27 BC - AD 14). There are five openings in the dome: a circular oculus and four square skylights. The dome has a span of 21.5 meters and is the largest known dome to have been built before that of the Pantheon. It is also the earliest preserved concrete dome.

The mortar and aggregate of Roman concrete was built up in horizontal layers laid by hand against wooden form-work with the thickness of the layers determined by the length of the workday, rather than being poured into a mold as concrete is today. Roman concrete domes were thus built similarly to the earlier corbel domes of the Mediterranean region, although they have different structural characteristics. The dry concrete mixtures used by the Romans were compacted with rams to eliminate voids, and added animal blood acted as a water reducer.

While there are earlier examples in the Republican period and early Imperial period, the growth of domed construction increases under Emperor Nero and the Flavians in the 1st century, and during the 2nd century AD. The opulent palace architecture of the Emperor Nero (54-68 AD) marks an important development. There is evidence of a dome in his Domus Transitoria at the intersection of two corridors, resting on four large piers, which may have had an oculus at the center. In Nero's Domus Aurea, or "Golden House", the walls of a large octagonal room transition to an octagonal domical vault, which then transitions to a dome with an oculus. This octagonal and semicircular dome is made of concrete and the oculus is made of brick. The radial walls of the surrounding rooms buttress the dome, allowing the octagonal walls directly beneath it to contain large openings under flat arches and for the room itself to be unusually well-lit. Another dome, made of wood, is reported in contemporary sources to have covered a dining hall in the palace, and may have been fitted such that perfume might spray from the ceiling. The dome perpetually rotated on its base in imitation of the sky. The expensive and lavish decoration of the palace caused such scandal that it was demolished soon after Nero's death and public buildings such as the Baths of Titus and the Colosseum were built in its place.

The most famous and best preserved Roman dome - and the largest - is that of the Pantheon, a temple in Rome built by Emperor Hadrian as part of the Baths of Agrippa. Dating from the 2nd century, it is an unreinforced concrete dome 43.4 meters wide resting on a circular wall, or rotunda, 6 meters thick. This rotunda, made of brick-faced concrete, contains a large number of relieving arches and is not solid. Seven interior niches and the entrance way divide the wall structurally into eight virtually independent piers. These openings and additional voids account for a quarter of the rotunda wall's volume. The only opening in the dome is the brick-lined oculus at the top, nine meters in diameter, which provides light and ventilation for the interior. The shallow coffering in the dome accounts for a less than five percent reduction in the dome's mass, and is mostly decorative. The aggregate material hand-placed in the concrete is heaviest at the base of the dome and changes to lighter materials as the height increases, dramatically reducing the stresses in the finished structure. In fact, many commentators cite the Pantheon as an example of the revolutionary possibilities for monolithic architecture provided by the use of Roman pozzolana concrete. However, vertical cracks seem to have developed very early, such that in practice the dome acts as an array of arches with a common keystone, rather than as a single unit. The exterior step-rings used to compress the "haunches" of the dome, which would not be necessary if the dome acted as a monolithic structure, may be an acknowledgement of this by the builders themselves. Such buttressing was common in Roman arch construction. It remained the largest dome in the world for more than a millennium and is still the world's largest unreinforced concrete dome.

Segmental domes, made of radially concave wedges or of alternating concave and flat wedges, also appear under Hadrian in the 2nd century and most preserved examples of this style date from this period. Hadrian's Villa has examples at the Piazza D'Oro and in the semidome of the Serapeum. Recorded details of the decoration of the segmental dome at the Piazza D'Oro suggests it was made to evoke a billowing tent, perhaps in imitation of the canopies used by Hellenistic kings. Other examples exist at the Hadrianic baths of Otricoli and the so-called "Temple of Venus" at Baiae. This style of dome required complex centering and radially-oriented formwork to create its tight curves.

In the 3rd century, Imperial mausolea began to be built as domed rotundas rather than tumulus structures or other types, following similar monuments by private citizens. Pagan and Christian domed mausolea from this time can be differentiated in that the structures of the buildings also reflect their religious functions. The pagan buildings are typically two story, dimly lit, free-standing structures with a lower crypt area for the remains and an upper area for devotional sacrifice. Christian domed mausolea contain a single well-lit space and are usually attached to a church. Examples from the 3rd century are the brick domes of the Mausoleum of Galerius, the Mausoleum of Diocletian, and the mausoleum at Tor de' Schiavi.

In the 4th century, Roman domes proliferated due to changes in the way domes were constructed, including advances in centering techniques and the use of brick ribbing. The so-called "Temple of Minerva Medica", for example, used brick ribs along with step-rings and lightweight pumice aggregate concrete to form a decagonal dome. The material of choice in construction gradually transitioned during the 4th and 5th centuries from stone or concrete to lighter brick in thin shells. The use of ribs stiffened the structure, allowing domes to be thinner with less massive supporting walls. Windows were often used in these walls and replaced the oculus as a source of light, although buttressing was sometimes necessary to compensate for large openings. The Mausoleum of Santa Costanza has windows beneath the dome and nothing but paired columns beneath that, using a surrounding barrel vault to buttress the structure.

Christian mausolea and shrines developed into the "centralized church" type, often with a dome over a raised central space. The Church of the Holy Sepulchre in Jerusalem, for example, was likely built with a wooden dome over the shrine by the end of the 4th century. The octagonal "Domus Aurea", or "Golden Octagon", built in 327 at the imperial palace of Antioch likewise had a domical roof, presumably of wood and covered with gilded lead.

Centralized buildings of circular or octagonal plan also became used for baptistries and reliquaries due to the suitability of those shapes for assembly around a single object. Baptisteries began to be built in the manner of domed mausolea during the 4th century in Italy. The octagonal Lateran baptistery or the baptistery of the Holy Sepulchre may have been the first, and the style spread during the 5th century.

The Church of the Holy Apostles, or Apostoleion, begun by Constantine in the new capital city of Constantinople, combined the congregational basilica with the centralized shrine. With a similar plan to that of the Church of Saint Simeon Stylites, four naves projected from a central rotunda containing Constantine's tomb and spaces for the tombs of the twelve Apostles. Above the center may have been a clerestory with a wooden dome roofed with bronze sheeting and gold accents.

With the end of the Western Roman Empire, domes became a signature feature of the church architecture of the surviving Eastern Roman - or "Byzantine" - Empire. The square bay with an overhead sail vault or dome on pendentives became the basic unit of architecture in the early Byzantine centuries, found in a variety of combinations. By the 5th century, structures with small-scale domed cross plans existed across the Christian world. Examples include the Mausoleum of Galla Placidia, the martyrium attached to the Basilica of San Simpliciano, and churches in Macedonia and on the coast of Asia Minor.

The first known domed basilica may have been a church at Meriamlik in southern Turkey, dated from 471-494, although the ruins do not provide a definitive answer. It is possible earlier examples existed in Constantinople, where it has been suggested that the plan for the Meriamlik church itself was designed, but no domed basilica has been found there before the 6th century. The Church of St. Polyeuctus in Constantinople (524-527) was apparently built as a large and lavish domed basilica similar to the Meriamlik church of fifty years before and to the later Hagia Irene of Emperor Justinian, by Anicia Juliana, the last descendent of the former Imperial House.

6th century church building by the Emperor Justinian used the domed cross unit on a monumental scale, in keeping with Justinian's emphasis on bold architectural innovation. His church architecture emphasized the central dome. Centrally planned domed churches had been built since the 4th century for very particular functions, such as palace churches or martyria, with a slight widening of use around 500 AD, but Justinian's architects make the domed brick-vaulted central plan standard throughout the Roman east. This divergence with the Roman west from the second third of the 6th century may be considered the beginning of "Byzantine" architecture.

The earliest existing of Justinian's domed buildings is the central plan Church of Saints Sergius and Bacchus in Constantinople, completed by 536. The dome rests on an octagonal base created by eight arches on piers and is divided into sixteen sections. Those sections above the flat sides of the octagon are flat and contain a window at their base, alternating with sections from the corners of the octagon which are scalloped, creating an unusual kind of pumpkin dome.

After the Nika Revolt destroyed much of the city of Constantinople in 532, Justinian had the opportunity to rebuild. Both the churches of Hagia Irene ("Holy Peace") and Hagia Sophia ("Holy Wisdom") were burnt down. Both had been basilica plan churches and both were rebuilt as domed basilicas, although the Hagia Sophia was on a much grander scale.

Built by Anthemius of Tralles and Isidore of Miletus in Constantinople between 532 and 537, the Hagia Sophia has been called the greatest building in the world. It is an original and innovative design with no known precedents in the way it covers a basilica plan with dome and semi-domes. Periodic earthquakes in the region have caused three partial collapses of the dome and necessitated repairs. The precise shape of the original central dome completed in 537 was significantly different than the current one and, according to contemporary accounts, much bolder. Byzantine chronicler John Malalas reports that the original dome was 20 byzantine feet lower than its replacement. One theory is that the original dome continued the curve of the pendentives, creating a massive sail vault pierced with a ring of windows. A more recent theory raises the shallow cap of this dome (the portion above what are today the pendentives) on a relatively short recessed drum containing the windows, which is mentioned in an account by Procopius. This first dome partially collapsed in 558 and the design was then revised to the present profile. The current central dome is about 32 meters wide. It contains 40 ribs which radiate from the center of the dome and 40 windows at the base of the dome between the ribs. The dome and pendentives are supported by four large arches springing from four piers. Additionally, two huge semi-domes of similar proportion are placed on opposite sides of the central dome, which themselves contain smaller semi-domes between an additional four piers. The brick dome also incorporated a wooden tension ring at its base to resist outward thrust and interrupt cracking, and iron cramps between the marble blocks of its cornice.

The octagonal Basilica of San Vitale in Ravenna, Italy, was completed in 547 and contains a terracotta dome. Hollow amphorae were fitted inside one another to provide a lightweight structure and avoid additional buttressing. The amphorae were arranged in a continuous spiral, which required minimal centering and formwork, but was not strong enough for large spans. The dome was covered with a timber roof, which would be the favored practice for later medieval architects in Italy although it was unusual at the time.

Justinian also tore down the aging Church of the Holy Apostles and rebuilt it on a grander scale between 536 and 550. The original building was a cruciform basilica with a central domed mausoleum. Justinian's replacement was likewise cruciform but with a central dome and four flanking domes. The central dome over the crossing had pendentives and windows in its base, while the four domes over the arms of the cross had pendentives but no windows. Justinian's Basilica of St. John at Ephesus and Venice's St Mark's Basilica are derivative of this design. More loosely, the Cathedral of St. Front and the Basilica of Saint Anthony of Padua are also derived from this church.

With the decline in the empire's resources following losses in population and territory, domes in Byzantine architecture were used as part of more modest new buildings. The large-scale churches of Byzantium were, however, kept in good repair. The upper portion of the Church of Hagia Irene was thoroughly rebuilt after an earthquake in 740. The nave was re-covered with an elliptical domical vault hidden externally by a low cylinder on the roof, in place of the earlier barrel vaulted ceiling, and the original central dome from the Justinian era was replaced with one raised upon a high windowed drum. The barrel vaults supporting these two new domes were also extended out over the side aisles, creating cross-domed units. These units became a standard element on a smaller scale in later Byzantine church architecture.

The Nea Ekklesia of Emperor Basil I was built in Constantinople around 880 as part of a substantial building renovation and construction program during his reign. It had five domes, which are known from literary sources, but different arrangements for them have been proposed under at least four different plans. One has the domes arranged in a cruciform pattern like those of the contemporaneous Church of St. Andrew at Peristerai or the much older Church of the Holy Apostles in Constantinople. Others arrange them in a quincunx pattern, with four minor domes in the corners of a square and a larger fifth in the center, as part of a cross-domed or cross-in-square plan.

The Cross-in-square plan, with a single dome at the crossing or five domes in a quincunx pattern, became widely popular in the Middle Byzantine period. This type of plan, with four columns supporting the dome at the crossing, was best suited for domes less than 7 meters wide and, from the tenth to the 14th centuries, a typical Byzantine dome measured less than 6 meters in diameter. For domes beyond that width, however, variations in the plan were required such as using piers in place of the columns and incorporating further buttressing around the core of the building.

In this period, domes were normally built to emphasize separate functional spaces, rather than as the modular ceiling units they had been earlier. Resting domes on circular or polygonal drums pierced with windows eventually became the standard style, with regional characteristics. The domes of the Church of the Holy Apostles appear to have been radically altered between 944 and 985 by the addition of windowed drums beneath all five domes and by raising the central dome higher than the others. The distinctive rippling eaves design for the roofs of domes begins in the 10th century. In mainland Greece, circular or octagonal drums became the most common while, in Constantinople, drums with twelve or fourteen sides were popular beginning in the 11th century.

The domed-octagon plan is a variant of the cross-in-square plan. The earliest extant example is the katholikon at the monastery of Hosios Loukas, built in the first half of the 11th century. Its square crossing bay is defined by four L-shaped piers which transition by conical squinches to an octagonal drum for the 9 meter wide dome. The smaller monastic church at Daphni, c. 1080, uses a simpler version of this plan.

Another variant of the cross-in-square, the "so-called atrophied Greek cross plan", also provides greater support than the typical cross-in-square by using piers set securely into the corners of the square naos. This design was used in the Chora Church of Constantinople in the 12th century after the previous cross-in-square structure was destroyed by an earthquake.

Byzantine domed buildings typically incorporated wooden tension rings at several levels within the structures, a technique frequently attributed as the later invention of Filippo Brunelleschi. Metal clamps between stone cornice blocks, metal tie rods, and metal chains were also used to stabilize domed construction. Timber belts at the bases of domes help to stabilize the walls below them during earthquakes, but the domes themselves remain vulnerable to collapse. The technique of using double shells for domes, although revived in the Renaissance, originated in Byzantine practice.

Byzantine domes and techniques of religious architecture spread to the surrounding Christian nations, such as Georgia and Armenia. Armenian church domes were initially wooden structures. Etchmiadzin Cathedral (c. 483) originally had a wooden dome covered by a wooden pyramidal roof before this was replaced with stone construction in 618. Churches with stone domes became the standard type after the 7th century, perhaps benefiting from a possible exodus of stonecutters from Syria, but the long traditions of wooden construction carried over stylistically. Some examples in stone as late as the 12th century are detailed imitations of clearly wooden prototypes.