The city, cited in the itineraries, is mentioned by Strabo (4.1.6), Pliny (3.17), Suetonius (Ner. 18), and Ptolemy (3.1.40); and recorded by Ammianus Marcellinus, Cassiodorus, and Nazario in the Panegyric to Constantine. A Celto-Ligurian oppidum of the Segusians, the city came under Roman rule in the Augustan age, and under Nero became a municipium at the time the province Alpium Cottiarum was instituted. Segusium was fortified during the Late Empire, and witnessed the siege of Constantine during the contest with Maxentius in A.D. 312.
The city plan shows characteristics of spontaneous formation, radiating from the primitive nucleus which excavation has localized near the present Porta Castello. At the intersection of the major roads in the forum indeterminate remains of important buildings have been found, including remnants of statues and a large votive base. From there the Gallic road continues toward the S and arrives at the summit of the hill, where there are ruins of ancient structures, perhaps large homes or public buildings. There is also an Arch of Augustus, with a single arch between pilasters and Corinthian columns at the corners. It bears an inscription and a figured frieze commemorating the friendship pact concluded with Rome in 9 B.C. by Julius Cozius, king of the Segusians and of the 14 cities of the Cottian Alps.
Little is known of the city in the early centuries of the Empire. Remains of roads and buildings furnish fragmentary and uncertain dates, except for clues from the presence of a bath building in the area of the present theater.
The Princeton encyclopedia of classical sites. Stillwell, Richard. MacDonald, William L. McAlister, Marian Holland. Princeton, N.J. Princeton University Press. 1976.
