Building Techniques and Materials | Roman Architecture | Second edition | (Part-01)

Building Techniques and Materials | Roman Architecture | Second edition | (Part-01)

Building Techniques and Materials | Roman Architecture | Second edition | (Part-01)
rome

 

Roman architects worked for the army or the civil service or were in private practice. The names of several architects are known, but unfortunately they are usually associated with a single building, for example M. Artorius Primus, the architect who rebuilt the theatre at Pompeii in the Augustan period (CIL 10.841). Decimus Cossutius, who designed the Olympieion at Athens in 174 bc, was a Roman citizen (Vitruvius, de Arch. 7, Praef. 15), but little more is known about him. A further complication is that although the names of celebrated architects, such as Apollodorus of Damascus (Dio, 69.4.1), survive, the buildings they designed are usually known by the name of their builder, not their architect, hence the Forum of Trajan. Little is known about the background of named architects such as Severus and Celer, architects and engineers of Nero’s Golden House (Tac., Ann. 5.42), and Rabirius (Martial, Epigr. 7.56), architect of the Flavian palace on the Palatine. Trajan’s architect, Apollodorus of Damascus, may well have been Greek to judge by what the emperor himself had to say. In an exchange of letters with Trajan, Pliny the Younger requested that an architect be sent from Rome to inspect the unfinished theatre of Nicaea. Trajan in his reply drily noted that the architects in Rome usually came from Greece anyway (Pliny the Younger, Epist. 10.39–40). As for portraits of famous architects the evidence is slight and conjectural. A bust in the Munich Glyptothek is often thought to be that of Apollodorus of Damascus, but the attribution is far from certain. Otherwise ancient architects are rarely commemorated, except on funerary monuments, such as the Hadrianic one of T. Statilius Aper, now in the Capitoline Museum, Rome. It shows Statilius himself, his wife, a child and, as a pun on his name, a boar. There are also some tombstones of builders, showing set-squares and plumb bobs.

Although we do not know a great deal about individual architects the Roman architectural profession seems to have been held in high regard. In Cicero’s eyes architecture was as important a profession as medicine and teaching (de off. 1.151). He recommends that jobs which incur people’s ill-will, like tax gathering and usury, are to be avoided. Some jobs are too vulgar for words, like those of fishmongers, butchers, cooks and poulterers. But it is quite acceptable to engage in a profession where a higher degree of intelligence is required, like architecture. To Vitruvius architecture was an admirable profession: “Since it is so great a profession encompassing many diverse accomplishments, I think that the only ones who can claim to be architects are those who have climbed the ladder from childhood, had a liberal education in the arts and sciences and have reached the pinnacle, the temple of architecture” (de Arch. 1.1.11).

Hero of Alexandria, who is thought to have lived in the later first century ad, is one of our most important sources for ancient technology. Pliny the Elder (ad 23-79) worked indefatigably on his encyclopaedic work, Naturalis Historia, which covers in 37 books everything from the planetary system to metals and stones. Frontinus, who was put in charge of Rome’s water supply (cura aquarum) in ad 97, gives a detailed account of every aspect of the subject, including reservoirs, aqueducts and piping. Our most detailed source for architecture is Vitruvius (fl. 27–23 bc), whose entire treatise has survived. In ten books he takes us through every aspect of an architect’s repertory: laying out a city, building walls of stone or concrete, designing a basilica, in particular his own at Fanum (de Arch. 5.1.6-10), and constructing temples in any of the three orders, Doric, Ionic or Corinthian. Elsewhere in his book he tells us about harmonics, especially when it comes to designing a theatre. He explains how to build baths, shipyards and harbours; how to decorate a ceiling with stucco; and what colour to paint your dining room. He tells us how to design aqueducts, sun-dials, water-clocks, water-mills, water-wheels and water-pumps, and if trouble is brewing how to build a ballista and a siege engine. Among other things he explains how a Roman architect draws up plans, elevations and shaded perspective drawings. A skilled draftsman, he says, ought to be able to produce coloured drawings to convey an impression of the work proposed.

Geometry also is a great help in architecture. It teaches us the use of the rule and compasses, and facilitates the layout and planning of buildings by the use of the set-square, level and plumb-line. Moreover by means of optics the light in buildings can be correctly drawn from fixed quarters of the sky. Also it is by arithmetic that the total cost of buildings is calculated and measurements are computed, and difficult questions of symmetry are solved by means of geometrical theories and methods. (Vitruvius, de Arch. 1.1.4)

To draft his plans an architect used dividers, folding foot-rules and calipers. The initial plans were probably made on wooden boards, parchment or papyrus, all perishable materials. Apart from the odd drawing on papyrus, such as the elevation of a portable shrine now in the Petrie Museum in London, the only actual plans to survive are those on marble or in mosaic, for example a marble plan of a tomb complex now in the Archaeological Museum at Perugia. A mosaic plan of a bath building, now in the Capitoline Museum at Rome (Figure 4.1), indicates the dimensions of the rooms in Roman feet (a Roman foot = c. 0.295 metre). It uses a number of conventions, most of which are still current, such as the way unbonded walls are indicated. Windows are shown as a pair of solid lines in the uninterrupted wall area, while doorways are shown as breaks in the wall. Plunge baths are shown in blue to represent water. The angle of the lettering in each case indicates the dimension meant. Thus in the room marked VII and XII, the VII indicates the width of the apse and the XII the overall length of the room along the other axis. Architects’ drawings included a whole range of conventions, such as triangles for staircases and dots for columns, seen on the Marble Plan of Rome. The Romans were of course well used to abbreviations and conventions, as a study of their inscriptions reveals.

A set of architect’s tools was found in the shop of Verus, an instrument maker at Pompeii (I.6.3), now in the Naples Archaeological Museum. For surveying, an instrument called a groma was used (Figure 4.2a). It consists of a pole driven vertically into the ground, with a horizontal bar at the top, at the end of which is a pivot. Attached to the pivot is a cross with four arms of equal length, which can revolve freely in an arc of 360o. From the end of each arm hangs a plumb-line and a fifth one hangs down from the centre of the cross. The surveyor aligned this fifth plumb-line to a cylindrical cippus on the ground which provided a fixed point from which to measure. By sighting across two opposite plumb-lines the surveyor could lay out either one or a number of squares or rectangles. Another indispensable aid in surveying, particularly by Roman engineers involved in laying out aqueducts, was the water

Figure 4.1  Mosaic plan of a bath building (Capitoline Museum, Rome): drawing.

 

Figure 4.2  Diagram to illustrate surveying instruments: (a) a groma; (b) a chorobates (water-level).

level (chorobates) (Figure 4.2b). It is described by Vitruvius (de Arch. 8.5.1–3), who says its wooden frame should be about 20 Roman feet (5.92 metres) long with cross-pieces to make it rigid. Then vertical lines should be drawn on the crosspieces and plumb-lines hung over each of them, so that when the plumb-lines correspond exactly to the vertical lines the instrument will be perfectly level.

Once the ground plan had been laid out, building the foundations could commence, followed by the floors and walls. It was only when some of the walling or flooring was in place that architects had an expanse wide enough to make the first large-scale detailed drawings of the architectural elements. The earliest come from the east. Full-scale profiles of the apophyge of a column shaft and the upper torus of the base can be seen incised into the platform of the second century bc Temple of Dionysus at Pergamum, renovated by Caracalla (Figure 4.3). Similar drawings have been found in the Temple of Athena at Priene and the Temple of Artemis at Sardis. A full-sized drawing of part of the pediment of the Temple of Jupiter at Baalbek (early first century ad) was found on one of the foundation stones (the socalled trilithon). The most complete examples of such drawings were found in 1979 on the podium walls of the adyton of the unfinished Temple of Apollo at Didyma, whose construction began at the end of the fourth century bc and continued into Roman times.1 The lines, which cover an area of about 200 square metres, are so fine as to be barely visible and were originally covered with red chalk to make them stand out. An examination of the drawings for the column bases shows that the first draft was usually geometrically perfect, but the drawings were then modified and refined on the wall by the architect. Parts of the columns

Figure 4.3  Pergamum (Bergama, Turkey), profile of the apophyge of a column shaft and the upper torus of the base, incised into the platform of the second century bc Temple of Dionysus.

were drawn at full size, although the full column was also shown at one sixteenth scale, thus allowing the entasis (a slight swelling in the middle of the shaft) to be set out. To do so on a full-scale drawing would have been impossible. These drawings, which survive only because the temple was never finished, give us an insight into how the details of large-scale buildings were designed. If the building had been finished the drawings would doubtless have been erased in the final polishing of the adyton walls. A similar drawing of the bottom storey of the façade was incised on the pavement in front of the amphitheatre at Capua. Mostly these drawings were incised onto the fabric of the building involved, but full-sized drawings of the Pantheon pediment were incised on the travertine pavement in front of the Mausoleum of Augustus about 700 metres away. Perhaps there was no comparable expanse of pavement on the site of the Pantheon itself, and in any case the Mausoleum of Augustus was much closer to the Tiber wharfs where the stone would have been landed.2

The next stage would have been to translate the drawings into the finished product. First the stone had to be brought from the quarry. Ancient quarrying was wasteful of stone, to judge by the archaeological evidence. First the block had to be freed on all four sides by means of drilling or picking, and then extracted by means of wedges placed under it. Equally laborious was the process of conveying the block to the building site. Squared blocks or columns could be dragged on a sled, on rollers or inside a device invented by Chersiphron, architect of the Archaic temple of Artemis at Ephesus, and his son, Metagenes (Figure 4.4b). This consisted of enclosing the block inside a large wooden wheel which could then be rolled to its destination without the risk of it getting bogged, as a cart’s wheels might. Vitruvius

 

Figure 4.4  (a) Device for transporting a column; (b) device for transporting a squared block: drawing.

records that in his own day Paconius used a similar device (de Arch. 10.2.11–14). Columns could be rolled (Figure 4.4a). To save weight, as much stone as possible was removed from the block in the quarry. However the block could not be finished completely, as this might involve damage to fragile mouldings in the course of transportation to the building site. To prevent damage and perhaps to aid handling, bosses were left projecting from the stone, to be removed once the building was complete. In the Temple of Apollo at Didyma both complete and incomplete column bases can be seen. On the unfinished column shafts lines were incised indicating the exact width of each fluting. In addition the depth and profile of each flute was incised into both ends of the shaft. These details were probably checked against the drawings on the wall of the adyton.

Several types of crane used on Roman building sites are described by Vitruvius (de Arch. 10.2.1–10). The simplest types used a jib consisting of two inclined beams joined at the top, with a capstan between them near the bottom (Figure 4.5). A pulley block with two wheels was hung from a stay-rope which passed over the two inclined beams. A rope from the capstan passed over the top wheel of the pulley block. The rope then ran down to a lower pulleyblock with a single wheel, around the wheel and back up to the lower wheel of the upper pulley block. It then ran down again to be attached to an eye on the lower block to which the load was attached. A simple system of this type was called trispaston, meaning that the ropes gave a reduction ratio of 1:3, so that a cable which could lift a tonne could be used to lift three tonnes. The beams were held in position by a stay-rope, but the jib could not exceed an angle of 30o from the vertical or it would topple. A more complicated type of crane could be

Figure 4.5  Crane with a reduction ratio of 1:3, called a tripaston

swung sideways, but its lifting power was limited. Multiple capstans were used for very large blocks, as shown on the base of the obelisk of Theodosius in Istanbul. The most powerful type of crane used a large tread-wheel to work the hoisting cable. Both the stay-ropes and the hoisting cable also used pulleys. This type of crane is illustrated in a remarkable relief from the tomb of the Haterii, now in the Vatican Museum. Several methods were used to attach the lifting-rope to the block, including the bosses mentioned earlier, U-shaped channels carved into the ends of the block, the ‘lewis’, and pincers of various designs. Once in position the blocks were joined together, not with mortar, but by metal clamps. The medieval practice of burrowing into the joints between blocks to extract the metal explains the pock-marked appearance of many ancient buildings, for example the Colosseum.3 Metal tie-bars seem to have been used as early as the time of Augustus according to the theory of Bauer, who examined a number of blocks from the Horrea Agrippiana (33–12 bc).4 Although the actual metal has disappeared the L-shaped cuttings survive and it is upon these that Bauer reconstructed tie bars at the base of the springings of the vaults.

An architect undertaking a big Imperial project would have had a large staff working under him. Frontinus records that as curator aquarum he had about two dozen specialist administrators in his headquarters, the statio aquarum (de Aquis 2.99–100, 116–119). These included engineers, architects, assistants, secretaries and clerks. There were also measurers, levellers, pipe-makers, keepers of reservoirs, inspectors and men to re-lay the streets which had been torn up to replace water mains. One can imagine that the architect in charge of an important imperial building project would have had at his disposal a similarly large staff to carry out his instructions. A mosaic, dating to the fourth century ad, in three registers from Wadi Ramel (now in Le Bardo Museum, Tunis) shows the construction of a building.5 At top left the architect holds a 5-foot (1.48 metres) measuring stick and to the right an assistant is shaping a small column with a hammer and chisel. Between them is a column capital, a set square, a plumb-bob and a stake for setting out lines. Below, a man brings mortar while another mixes it. At the bottom a horse-drawn cart is bringing another column to the site.

When the plans had been drawn up and the site selected the ground had to be prepared for the building. The Romans did not necessarily remove all buildings from the site. Often earlier foundations were encased or vaulted over, or an older building was filled with rubble and incorporated into the foundations. For example, the Esquiline wing of the Nero’s Domus Aurea was used in the foundations of the Baths of Trajan (Figure 8.1). At Ostia the galley which brought Caligula’s obelisk to Rome was filled with concrete and used as the foundation for Claudius’ lighthouse (Suet., Claud. 20). While the Greeks tended to take advantage of natural features when planning their temples and theatres, avoiding large-scale alterations to the terrain, the Romans did not hesitate to make immense excavations to lower the ground level or pile up mountains of earth to create artificial terraces. To build Domitian’s palace on the Palatine in Rome large amounts of earth were excavated to create a flat platform for the lower part of the building and earth was then piled up behind concrete retaining walls to level the upper part. Domitian’s engineers and later those of Trajan must have been skilled in the art of excavation because they cut away the spur of land which linked the Capitoline and Quirinal hills, the site of the later Forum and Markets of Trajan. The sheer scale of the enterprise can be judged by the inscription which records that the column was built ‘to show how high a mountain … had been cleared away’ (Figure 8.2). When the ground was ready foundation trenches were dug, either to bedrock or to an adequate depth, sometimes as much as 5 or 6 metres. Foundation walls were mainly of unfaced concrete, but stone was used where loads were particularly heavy. Under the Colosseum there is a ring of concrete footings 8 metres deep. The Pantheon rests upon a solid ring of concrete, c. 7 metres wide × 4.5 metres deep.

At this point something should be said about Roman concrete. The Romans did not possess easily accessible quarries of marble or smooth limestone, as did the Greeks. The most common building materials in the vicinity of Rome were mainly soft, volcanic stones. It was probably this factor above all which caused the Romans to adopt a mortared rubble construction which was to develop into a durable concrete. Campania was probably the place where the first mortared walls were built. A framework of limestone blocks with rubble between, held together by lime and clay was used in walls at Pompeii as early as the fourth century bc. By the third century bc the Pompeians had developed a strong mortar using lime and pozzolana (pulvis Puteolanus), a volcanic dust found in the region of Pozzuoli.6 The use of pozzolana enabled them to dispense with the framework and build walls entirely of mortared rubble, except for the quoins where stone and later brick were used. Today the term ‘pozzolana’ is a generic term for volcanic ash, but the Romans did not think of what we call pozzolana as a single substance. They found that they could make a strong mortar using a local pozzolana which they called harena fossicia (Vitruvius, de Arch. 2.5.1). However, they believed that pulvis Puteolanus was better for breakwaters and harbours. The walls of early structures consisted of a filling of small stones (caementa) between two facing walls. The binding material was a simple lime mortar, which was made by burning limestone (CaCO3) to obtain quicklime (CaO), which was slaked to produce calcium hydroxide (Ca(OH)2). Sand was then added and on evaporation crystals of calcium carbonate (CaCO3) formed, thus completing the cycle.

The Romans classified their concrete according to the facing used. The three main facings, in chronological order, are: opus incertum, an irregular facing of small stones; opus reticulatum, a neater facing of small pyramidical-shaped stones with the square face laid diagonally; and opus testaceum, brick or tile facing (Figure 4.6). The term opus incertum was applied to the earliest concrete facing because of the irregular stones used. For a long time it was dated to the time of Sulla, because Delbrueck, in an authoritative publication, dated opus incertum to 100–80 bc.7 More recent work suggests that the technique began much earlier. However, the substantial remains of concrete walling in Via Marmorata, which have long been regarded as belonging to the Porticus Aemilia, an enormous warehouse known to have been built in 193 bc with restorations in 174 bc (Figure 1.13), have recently been identified as navalia (ship-yards), which for the moment throws the whole question of early opus incertum into doubt.8  If the old identification can be maintained it is clear that highly advanced concrete structures were being built nearly a hundred years before the time of Sulla, and that therefore the period experimentation with concrete must be moved back to the third century bc (Figure 4.7).

A notable example of the use of opus incertum is the Temple of Magna Mater on the Palatine, which is known to have been built in the years 204–191 bc (Livy, 29.3.2) and twice rebuilt after fires in 111 bc and ad 3 (Valerius Maximus, 1.18.11). On excavation three building phases were revealed, the earliest using opus incertum, the next opus quasi-reticulatum and the latest belonging to the surviving building. Yet the excavator, P. Romanelli, following Delbrueck, maintained that a temple could not possibly have been built of opus incertum at such an early date, and that therefore the opus incertum must date to the rebuilding of 111 bc.9 F. Coarelli, in an article written in 1977 warning against the ‘myth of Sulla’ whereby so many Republican buildings were dated to the time of the dictator, noted that there was a shortage of money to finance the building of the temple in 204 bc and that opus incertum may well have been an economy.10 However, Coarelli’s work is also being revised.11 In 1940 remains of opus incertum walling were discovered at the foot of the Capitoline Hill. These have been identified as a terrace wall near the Aequimalium erected by the Censors in 189 bc

Figure 4.6  Diagram to illustrate Roman concrete facings. Top left: opus incertum, second century bc; top right: opus reticulatum, mainly later first century bc and first century ad; below: opus testaceum, mainly mid first century ad onwards.

to support the hill. Here the opus incertum has a facing of small irregular pieces of stone in grey mortar. Another structure of the same period is the viaduct extending from the Temple of Saturn to the Capitolium built in 174 bc. Another example of opus incertum is the Porticus Metelli, which was built in 146 bc around the Temples of Juno Regina and Jupiter Stator. One of the most celebrated examples of the use of opus incertum is the Sanctuary of Fortuna at Palestrina, which was rebuilt in the late second century bc (Figure 1.20).

The transition to opus reticulatum may also have begun much earlier than was previously believed, perhaps in the late second century bc. This was a time when the facing stones became squarer and were laid along almost straight diagonal joints. The term opus quasireticulatum is applied to this technique and examples of it can be seen in the rebuilding of the Lacus Iuturnae in the Roman Forum (117 bc), the Horrea Galbana (c.108 bc) and the House of the Griffins on the Palatine (c. 100 bc). Its development in Rome during the late second century bc may have been accelerated by the need to provide amenities for a rapidly growing population. Coarelli suggests that building methods may have been industrialised during these years, perhaps as a method of standardising components in order to speed construction work. Certainly the time of the Gracchi seems to have been a period of extraordinary expansion and energy both in Rome and Italy. The earliest example of true opus reticulatum, a network of perfectly regular facing stones laid diagonally, is found in the Theatre of Pompey in Rome, which was built between 61 and 55 bc. The technique became extremely common at the time of Augustus, indeed universal according to Vitruvius (de Arch. 2.8.1), who with

Figure 4.7  Rome, Porticus Aemilia.

 

typical conservatism says that opus reticulatum walls are apt to crack along their joints and that opus incertum is stronger. The sides of the tesserae which composed opus reticulatum varied in size from 5.00 to 6.50 centimetres in late Republican and early Augustan work to 8.00–10.00 centimetres in Tiberian work. The quoins were usually tufa until the middle of the first century ad, when they were regularly of brick.

Reticulate work of the later Augustan period shows a high degree of precision despite the fact that it was mostly hidden under a veneer of marble, limestone or stucco (Figure 4.8). However, particularly outside Rome, many examples of polychrome opus reticulatum have turned up which do not seem to have been concealed by a veneer. The high survival rate of Roman concrete monuments is largely explicable in terms of the great strength and durability of lime-pozzolana cement which reacts in a much more complicated way than a simple lime mortar. Its active ingredients were amorphous and vitreous silicates and aluminates which combined with lime to form hydrated silicate of calcium and other aluminate/silicate complexes. The fact that these did not need to lose water by evaporation, but incorporated it into their structure, enabled lime-pozzolana cement to set under damp conditions or even under water. Vitruvius recognised the remarkable properties of pozzolana: “When it is mixed with lime and rubble it not only lends strength to buildings of other kinds, but even when piers are constructed in the sea, they set hard under water” (de Arch. 2.6.1).

The next major development in Roman concrete was the introduction of brick or tile facing (opus testaceum). At this point a distinction should be drawn between baked bricks (testae) and unbaked bricks (lateres). Vitruvius mentions two types of brick, baked (coctus) and unbaked (crudus), when discussing city walls (de Arch. 1.5.8). Unbaked brick, according

Figure 4.8  Pompeii, wall of polychrome opus reticulatum.

to Vitruvius, was used from the earliest times in the Mediterranean region and continued to be used throughout the Roman Empire. An imposing stretch of late fourth century bc walling, 8.25 metres high in parts, found at Gela in Sicily is of unbaked brick on a stone foundation.12 According to Vitruvius (de Arch. 2.3.3) there were three sizes of unbaked brick. One size, pentedoron or five palms square, was used by the Greeks in public buildings. Unbaked bricks, measuring 44 centimetres square × 6 centimetres high, found in sites such as Berenice (Benghazi, Libya), are presumably of this type. He goes on to say that a somewhat smaller brick, tetradoron or four palms square (c. 35 centimetres), was commonly used by the Greeks in domestic or private buildings. The third type, which the Greeks called Lydian, was a foot and a half long (0.444 metres) and one foot wide (0.296 metres) and was used by the Romans. Although the type of brick normally referred to by Vitruvius was unbaked, he mentions a regulation in Rome which restricted the thickness of walls abutting public property to one and a half feet (de Arch. 2.8.17). As this thickness of unbaked brick will support only one storey, he concludes that baked brick must instead be used in these circumstances, given the need for tall buildings to cope with population pressure in Rome. These were not the only factors involved in the change from unbaked to baked brick. Unbaked brick was not a material able to withstand the frequent Tiber floods. A building collapsed in the flood of 54 bc, because the unbaked bricks became soaked through (Dio, 39.62.2). Whether of baked or unbaked brick apartment blocks in Rome frequently collapsed in any case or caught fire during the Late Republic. Publius Licinius Crassus, the richest man in Rome in his day, made his money by buying them up (Plutarch, Cras. 2.4). Collapsing apartment blocks remained a hazard in Rome in imperial times to judge by Juvenal, who complained of rental conditions in Rome: “The manager of the apartment building stands in front of the collapsing structure and, while he conceals an old gaping crack, he tells you to sleep soundly even though collapse is imminent” (Sat. 1.3.194–6). Cicero, who like many other senators depended upon rental property for income, jokes: “Two of my shops have fallen down, and the rest have cracks; and so not only the tenants, but even the mice have moved out” (Cicero, Att. 14.9).

 

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