Vitruvius[[2412]] gives elaborate instructions about the preparation of the clay for sun-dried bricks, and counsels in the first place a careful choice of earth, avoiding that which was sandy or stony or full of loose flints, which made the bricks too heavy, and so liable to split and fall out when affected by rain; it also prevented the straw from binding properly. Clay which was either whitish or decidedly red (from a prevalence of ochre) was preferred, and that combined with coarse sand (sabulo masculus) made light tiles, easily set. The process of manufacture was a very simple one. The clay was first carefully cleaned of foreign bodies, and then moistened with water and kneaded with straw. It was then moulded by hand or in a mould or frame of four boards, and perhaps also pressed with the foot.[[2413]] The bricks were then dried in the sun and turned as required, the usual process also adopted in the modern brickfield. Some bricks actually bear the marks of the feet of animals and birds which had passed over them while the clay was soft, and there is one in the Shrewsbury Museum with the imprint of a goat’s feet. Others at York and Wiesbaden show the nails of a boy’s shoes.[[2414]] These impressions of feet (where human) may also be referred to the practice of using the feet to knead the bricks.
The bricks were then ready for use, but were kept for two years before being employed, otherwise they were liable to contract, which caused the stucco to break off and the walls to collapse. At Utica, Vitruvius tells us, they had to be kept five years, and then could only be used if passed by a magistrate. Altogether, much care was taken in their preparation, and it was generally considered that spring and autumn were the most favourable times for making them, probably because they dried more slowly and were less liable to crack during the operation. In summer the hot sun baked the outer surface too fast, and this appeared dry while the interior was still moist, so that when the inside dried the outside contracted and split.[[2415]] It was also, of course, advisable to avoid seasons of rain and frost. But the bricks could not be properly tested until they had undergone some exposure to the weather, and for this reason Vitruvius recommends the employment of old roof-tiles where possible in building walls.[[2416]]
For baked bricks the processes must have been much the same, with, of course, the addition of the baking in the furnace. Existing Roman bricks are nearly always of well-tempered clay and well baked; but the clay exhibits a great variety of colour—red, yellow, and brown. The paste is remarkably hard, breaking with an almost vitreous fracture, and sometimes shows fragments of red brick (pozzolana) ground up with it to bind it together, and prevent warping. This may be seen in the Flavian Palace on the Palatine, and in an archway in the Aurelian Wall near the Porta Latina. As an instance of varieties of brick found in the same building, Nero’s Aurea Domus may be cited.[[2417]] The durability of Roman tiles is ascribed to their careful preparation and seasoning, which give them a much longer life than modern tiles; hence they were frequently used up again in early mediaeval buildings and in Romanesque churches in England, as at St. Albans, St. Mary-in-Castro, Dover, and St. Botolph’s and Holy Trinity, Colchester.[[2418]]
During the period of the Republic private houses and public buildings alike were built of unburnt brick in Rome, as we learn from the words of Dio Cassius,[[2419]] Varro,[[2420]] and Cicero[[2421]]; Varro speaks of domus latericiae, and Cicero of “the brick (latere) and concrete of which the city is constructed.” After the Republican period this material was still employed outside Rome with burnt-brick cornices,[[2422]] but even this was exceptional. Pliny mentions walls of sun-dried bricks at Arretium and Mevania.[[2423]] Henceforth, then, burnt brick was employed more and more as Rome grew more populous.[[2424]] In Vitruvius’ time (the beginning of our era) the materials used for building were stone for substructures, burnt brick (structura testacea) for the outer walls, concrete for the party-walls, and wood for the roofs and floors. He explains the cessation of the use of unburnt brick as due to the legal regulations of his time, which prohibited party-walls of more than 1½ foot in thickness, and unburnt bricks could only support one story above them in that size.[[2425]]
Baths, either public or private, walls and military fortifications, were built of bricks, the latter being thus better able to resist attacks than if they were of stone. Temples, palaces, amphitheatres, the magnificent aqueducts and the cisterns with which they communicated, were also usually of this material. Of these, numerous remains exist in Rome and other places, such as Cumae and Pozzuoli. The aqueduct made by Nero from the Anio to Mons Caelius is of brick, that of Trajan partly so; the aqua Alexandrina of Severus Alexander (A.D. 229) and that existing at Metz are wholly of brick, and so are the castella or reservoirs made by Agrippa when he constructed the Julian conduit over the Marcian and Tepulan.[[2426]] It is true that Augustus boasted that he had found Rome of brick and left it marble[[2427]]; but it must be remembered, firstly, that Suetonius uses the term latericiam, which may denote unburnt brick; secondly, that the phrase is probably to be limited to public buildings and monuments, in which there was an increased use of marble for pillars and roofs. For walls brick and concrete continued to be used, as in private buildings, with a covering of stucco in place of marble incrustation.
In the first century of the Empire brick-making was brought to perfection, and its use became universal for private and public buildings alike; the mortar of the period is also of remarkable excellence. The Romans introduced brick-making wherever they went; and even their legions when on foreign service used it for military purposes. But of pure brick architecture, as we see it, for instance, in the Byzantine churches of Northern Italy, there was no question until comparatively late times. It was always covered over with marble or stucco until the second century of the Empire. Examples of sepulchral buildings wholly in brick, of the time of Hadrian, may be seen in the tomb before the Porta San Sebastiano at Rome, known as the temple of Deus Rediculus. This has Corinthian pilasters with a rich entablature, red bricks being used for architectural members, yellow for the walls; the capitals are formed of layers of bricks. Of Hadrian’s time are also the guard-house of the seventh cohort of Vigiles across the Tiber, of which a small part remains, and the amphitheatrum castrense on the walls of Aurelian.[[2428]]
One of the most remarkable instances of Roman brick construction is the Pile Cinq-Mars, as it is called, a tower still standing on the right bank of the Loire, near Tours. It is about 95 feet high and 13 feet square, expanding at the base, being built of tiles to a depth of 3 feet each side, with a body of concrete; the tiles are set in mortar composed of chalk, sand, and pounded tiles. On one side there are eleven rectangular panels with tile-work of various patterns, like those on the flue-tiles (see p. [348]), and as also seen on the Roman wall at Cologne; the patterns include squares, triangles, and rosettes. The history and purpose of this building are quite unknown.[[2429]]
At Pompeii bricks are used only for corners of buildings or doorposts, and sometimes for columns, as in the Basilica and the house of the Labyrinth.[[2430]] There are also late examples of brick columns with capitals in tiers of bricks as in the tomb mentioned above. Brick walls are not found, but bricks occur as facing for rubble-work. These are less than an inch thick, triangular in form, with the hypotenuse (about 6 inches long) showing in the face of the wall. Sometimes fragments of roof-tiles are used (cf. p. [334]). The earlier bricks contain sea-sand, and have a granular surface; the later are smooth and even in appearance. Later, what is known as opus mixtum (see below) is used, as in the entrance of the Herculaneum gate; this implies courses of stone and brick alternating,[[2431]] which, as we have seen, was common in military works, as in the Roman walls in Britain. In this country, owing to the absence of good material for concrete, the use of stones or brick throughout for building was general from the first; hence, too, the bricks are always flat and rectangular in form (bipedales).[[2432]]
The arrangement of triangular bricks (made by dividing a medium-sized brick into four before baking), laid flat in regular horizontal courses, is characteristic of the earliest examples of Roman methods. It is found in the Rostra (44 B.C.) and in the Regia (35 B.C.), the earliest existing examples.[[2433]] The back wall of the Rostra is of concrete faced with triangular bricks 1½ inch thick, the sides 10 inches long. The same arrangement may be seen in the Pantheon, in the Thermae of Diocletian, and in some of the aqueducts (see below). The brickwork in the Pantheon was formerly thought to belong to the building of Agrippa in 27 B.C., but has been now shown to belong to the second century.[[2434]] At Ostia, in the temple of Honos and Virtus, the walls are built of triangular bricks or with red and yellow bricks with moulded cornices.
