When the Romans came, Vaison was the capital of the Voconces, a people of Celtic origin, allied with the Romans. The romanization of the region was then that much easier as the town of "Vasio" benefited from the status of a federate city, which conferred on it notable advantages and privileged relations with Rome.

The city progressively developed over the plain on the right bank of the Ouveze river, erecting numerous and rich residences and public buildings (theaters, baths).