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]