The principal monuments of Roman architecture belong chiefly to the period between 100 B.C. and A.D. 300, including the Colosseum (A.D. 70–82), the Pantheon (A.D. 118–125; see under pantheon), and the Baths of Caracalla (c.A.D. 215). Beginning with the reign of Augustus (30 B.C.–A.D. 14), the Roman architectural output proceeded on a vast scale to accommodate the needs of the rapidly expanding empire. Provincial towns were laid out according to logical plans, particularly in North Africa. In Syria, arcaded streets were built.
Each town's focus was the forum, or open public square, surrounded by colonnades and the principal buildings in axial arrangement. The great forum in Rome itself was built in stages, as each emperor sought to glorify his achievements. The last large forum to be built was that of Trajan (2d cent. A.D.), and was the most extravagant. Within each forum, a temple, conforming to Etruscan type, was usually elevated on a high base with steps ascending to a deep portico. Since the temple was to be seen only from the front, the Roman architect utilized pilasters or engaged columns along its sides. This pseudoperipteral type is seen in the Maison Carrée (1st cent. A.D.) at Nîmes, France. Examples of circular temples include the temple of Vesta at Tivoli (1st cent. B.C.) and the 3d-century temples of Jupiter at Split and Venus at Baalbek.