Arretium sided with Marius in the Roman Civil War, and the victorious Sulla planted a colony of his veterans in the half-demolished city, as "Arretium Fidens" ("Faithful Arretium").
Leta 311 pred našim štetjem so mesto osvojili Rimljani, Arretium je postal vojaška postojanka na poti preko Cassia, širitve Rima v porečje reke Pad.