In many buildings a domed or vaulted roof was con-structed. These constructions are based on the arch;
a vault is an elongated arch and a dome is a series of arches meeting at their highest point. The Romans did not invent these techniques, but they developed them and used concrete for the first time. The com-bination of these elements made Roman architec-ture distinct from Greek. For example, it was the use of vaults and arches that allowed the Romans to build freestanding theaters, whereas Greek ones were usually built into a hillside for support.
The true arch built of voussoirs (wedge-shaped stones fitted together to form the shape of the arch and held in place by lateral pressure) was a relatively late development in western architecture. Arches were known in Egypt from the 6th century BC, but the Romans began to use them only in the 3rd century BC. The width that can be spanned by an arch or bar-rel vault is unlimited, but the wider arches or vaults 4.23 Reconstruction at Mehring villa of a window with
an iron grille.
4.24 A cast of a wooden window shutter at the Villa of the Mysteries, Pompeii.
are, the higher they become (see “Bridges” in chapter 5). To achieve greater spans with lower ceilings, bar-rel vaults were built side by side, supported on side walls pierced with arches. Groined vaults were used more often, consisting of two barrel vaults intersect-ing at right angles. These vaults could span a large rectangular area, with supporting pillars needed only at the four points of intersection. By increasing the number of intersecting vaults, a dome shape could be achieved, and by combining various vaults and arches, a new style of architecture developed. A strik-ing example of this is the Colosseum, built at Rome in the late 1st century. Although its exterior was dec-orated with Doric, Ionic and Corinthian columns, the building is essentially a Roman structure of arches and vaults.
The use of concrete for arches and vaults necessi-tated extremely skilful and precise carpentry during construction. To build a concrete arch, the centering (the wooden template, supported on wooden scaf-folding, over which the arch was formed) had to function as shuttering for the poured concrete. It was removed once it was safe to do so, usually after about two weeks. Not only did the centering have to be of precisely the correct shape, but it also had to be strong enough to sustain the weight of the
con-crete until it had set. An added difficulty in building vaults and domes was the construction of centering with a complex shape using the same standards of precision and strength. The use of hollow terracotta vaulting tubes (tubi fittili) was very popular in the construction of barrel vaults from the 2nd century, particularly in north Africa.
Most commonly buildings were roofed with tiles over a timber framework. There were two types of roof tile, the tegula (pl. tegulae) and imbrex (pl.
imbrices) which were used in combination to form a weatherproof roof. Tegulae were flat, slightly taper-ing subrectangular tiles with a flange along both long sides. Imbrices resembled slightly tapering tubes that had been cut in half lengthways. The tegulae were fixed side by side and the imbrices were fixed over the gaps between the tegulae. Since the tiles were slightly tapering, each row of tiles could overlap the row below to eliminate gaps. (See also “Tiles” in chapter 8.)
Throughout the empire there was a great deal of variation in roofing methods. Although roofs tiled with tegulae and imbrices must have been relatively common, roofing slates made of various stones were used in areas where such stone was available, and sometimes slates were chosen for decorative reasons.
4.25 Replicas of Roman tegulae (left) and imbrices (right).
In many provincial areas a large proportion of build-ings would have been thatched, and the use of wooden shingles is known. In drier areas in the east-ern provinces many domestic houses had flat roofs of mud brick supported on timber or vaulting.
Chimneys were not used in any area; smoke from hearths and ovens escaped through holes in the roof.
Floors
Apart from the suspended concrete floors of the hypocausts, there was a great variation in flooring methods. Beaten earth floors were found in the poorest houses, but they could also be of stone blocks, tiles (sometimes laid in a herringbone pat-tern—opus spicatum) or of wood.
Another common method was concrete made with opus signinum for resistance to damp. Floors
could be surfaced with small cubes of stone, tiles or other materials set in concrete to form a tessellated surface, or with very small cubes of various materials to form a mosaic. Floors of mortar (signina) were also mixed with crushed tile or stone to give a utili-tarian surface. Mortar floors could also be decorated with larger fragments of colored stone (crustae).
Heating
One distinctive Roman feature was the underfloor heating system called the hypocaust, which was pos-sibly invented in the 1st century BC. Heated rooms had floors supported on brick or stone piers (pilae), or occasionally had stone or brick-lined channels built into a solid foundation (channelled hypocaust), in order to allow the passage of hot air. The floor itself was of thick concrete, which warmed up slowly
4.26 Stone-built flue of a hypocaust through which hot air passed from the furnace and under the floor. The floor beyond is supported on piers of tiles (pilae).
but retained heat. Hot air and gases from the fur-nace passed beneath the floor, providing the main heating, and then passed through tile-lined channels or flues in the walls, before escaping under the eaves of the roof. (See also box tiles in chapter 8.)
The hypocaust system was expensive in terms of labor and fuel, and the temperature was not easily controlled and could be very uneven, depending on the design of the particular hypocaust. Probably because of its cost, such a system usually heated only a few rooms within domestic houses, but it was used to great effect in public and private baths. In rooms without a hypocaust, charcoal-burning braziers pro-vided the heating.
In baths, the hypocaust was designed for mini-mum heat loss, so that the hot air first passed to the hottest rooms (laconicum, sudatorium and caldarium), and then, as it cooled, to the next hottest and so on.
A boiler over the furnace provided hot water.
Lighting
Candles, torches and lamps were the main forms of lighting. Torches were used largely outdoors, and candles of beeswax and tallow, and candlesticks, were used in provinces where olives were not culti-vated. Lamps were commonly used for lighting from the 1st century BC, using olive oil as fuel. They were often placed on stands. Luxurious examples of bronze lamp stands and candelabra are known.
Lamps were made of many materials, mainly pot-tery, but also bronze, lead, iron, gold, silver, glass and stone. (See chapter 8 for pottery lamps).