page_title: History of Roman and Byzantine domes
section_title: Late Republic and early Imperial period
hierarchical_section_title: History of Roman and Byzantine domes / History / Late Republic and early Imperial period
caption_attribution_description: Deutsch: Baia-Das Gebiet der römischen Termalbäder Italiano: Baia-Complesso Termal Romano English: Compex of the roman thermapbath
context_page_description: Domes were a characteristic element of the architecture of Ancient Rome and of its medieval continuation, the Byzantine Empire. They had widespread influence on contemporary and later styles, from Russian and Ottoman architecture to the Italian Renaissance and modern revivals. The domes were customarily hemispherical, although octagonal and segmented shapes are also known, and they developed in form, use, and structure over the centuries. Early examples rested directly on the rotunda walls of round rooms and featured a central oculus for ventilation and light. Pendentives became common in the Byzantine period, provided support for domes over square spaces.
  Early wooden domes are known only from a literary source, but the use of wooden formwork, concrete, and unskilled labor enabled domes of monumental size in the late Republic and early Imperial period, such as the so-called "Temple of Mercury" bath hall at Baiae. Nero introduced the dome into Roman palace architecture in the 1st century and such rooms served as state banqueting halls, audience rooms, or throne rooms.
context_section_description: 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 cold rooms of the Terme Stabiane and the Terme del Foro. These domes are very conical in shape, similar to those on an Assyrian bas-relief found in Nineveh. At a Roman era tepidarium in Cabrera de Mar, Spain, a dome has been identified from the middle of the 2nd century BC that used a refined version of the parallel arch construction found in an earlier Hellenistic bath dome in Sicily. According to Vitruvius, the temperature and humidity of domed warm rooms could be regulated by raising or lowering bronze discs located under an 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.
  Varro's book on agriculture describes an aviary with a wooden dome decorated with the eight winds that is compared by analogy to the eight winds depicted on the Tower of the Winds, which was built in Athens at about the same time. 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 necessary for dome centering and support during construction, and they seem to have eventually become more efficient and standardized over time.
  Domes reached monumental size in the Roman Imperial period. Although imprints of the formwork itself have not survived, deformations from the ideal of up to 22 centimeters (8.7 in) at the so-called "Temple of Mercury" in Baiae suggest a centering of eight radiating frames, with horizontal connectors supporting radial formwork for the shallow dome. The building, actually a concrete bath hall dating from the age of Augustus (27 BC – 14 AD), has the first known large Roman dome. There are five openings in the dome: a circular oculus and four square skylights. The dome has a span of 21.5 meters (71 ft) and is the largest known dome built before that of the Pantheon. It is also the earliest preserved concrete dome.
caption: Flooded ruins of the so-called "Temple of Mercury" in Baiae
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