Segusium and the ancient Roman remains of Susa

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Cottius, wise and far-sighted Cottius, king of the Cottians. When Caesar was assassinated in 44 B.C., and Rome plunged into a bloody civil war, some of the Gallic tribes settled in Northern Italy took the opportunity to rebel. The Salassians on several occasions barricaded themselves in the Alpine passes, in the hope of getting free from the legions, but they were finally subdued with the foundation of Augusta Praetoria. Cottius had well understood that the Romans were a too powerful enemy, although they were engaged in internal political disputes. Moreover, even during the reign of his father Donno, the Celto-Ligurian tribe of the Cottii settled in the Susa Valley had chosen the path of cooperation. In 61 B.C. they had made an alliance treaty that allowed Caesar’s legions to safely walk along the Gaul route to the Montgenèvre Pass.

This had allowed the Cottians to prosper in peace for decades; so, Cottius decided not to break his father’s ancient treaty (foedus). Moreover, when Augustus became emperor in Rome, the king of the Gauls reinforced the old friendship. In 13 B.C. he renewed the alliance and to celebrate the event commissioned a monumental arch in honor of the emperor in the capital city of Segusium, today Susa (9-8 B.C.).

View of the Arch of Augustus from the Roman Aqueduct (improperly called the Gratian Baths; 4th century AD).

A monument celebrating an alliance: the Arch of Augustus in Segusium

The Arch of Augustus in Susa was constructed using local limestone and marble by Italic workers. It has a unique arcade with a barrel vault. The archivolts are supported by pilasters with Corinthian capitals, a motif also found in four columns on the outer corners of the structure. Above the architrave are developed an entablature with frieze and an attic with a dedicatory inscription.

Imp(eratori) Caesari Augusto, Divi f(ilio), pontifici maxumo, tribunic(ia) potestate XV, imp(eratori) XIII ; M(arcus) Iulius, regis Donni f(ilius), Cottius, praefectus ceivitatium quae subscriptae sunt: Segoviorum, Segusinorum, Belacorum, Caturigum, Medullorum, Tebaviorum, Adanatium, Savincatium, Egdiniorum, Veaminiorum, Venisamorum, Iemeriorum, Vesubianorum, Quariatium et ceivitates quae sub eo praefecto fuerunt1.

The four bas-reliefs in the frieze illustrate the ceremonies of the alliance between Cottius and Augustus: an animal sacrifice for purification purposes (suovetaurilia); a ritual scene for the Dioscuri; the representatives of the fourteen peoples that composing the Cottii; the last scene, unfortunately, is now unreadable2. It is worth noting that the Susa monument is an exception. It is a rare example of an arch celebrating an alliance, not a military victory of Rome. Cottius had it built in a sacred area, as demonstrated by the presence of a Celtic altar located nearby, attesting the importance of the event to which it is dedicated.

Near the Aqueduct there is a Celtic altar, carved from rock, with cup marks

The Roman rule

The Cottian kings ruled Susa for two more generations. Cottius’ grandson, in fact, had no heir, and after him Rome administered the province directly. The city thus became an important settlement placed to control the road leading to Gaul. Romans built an amphitheater (2nd century) and the city forum, with an elevated temple, the remains of which are located at Piazza Savoia.

The Roman amphitheater of Segusium

In the 3rd century the settlement was incorporated within the city walls still visible, which include the characteristic entrance gates (Porta Savoia, Porta di Francia, Porta di Piemonte).

Porta Savoia is an example of Roman military architecture. At its side is the Cathedral of San Giusto

The triangular-shaped plan aimed at defending the city from barbarian incursions.

Samuele Corrente Naso

Map of places


  1. Corpus Inscriptionum Latinarum, V 7231. ↩︎
  2. P. Pensabene, Arco di Susa: forme della decorazione architettonica, in L’arco di Susa e i monumenti della propaganda imperiale in età augustea, Anno LII, Susa, SEGUSIUM – Società di Ricerche e Studi Valsusini, luglio 2015. ↩︎
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