Vetralla's dominating fortified position in the heart of Etruscan territories has been continuously occupied since the Early Middle Ages. The Roman site, two kilometers distant, was a posting station on the Via Cassia; some ruins of walls and paving at S. Maria di Forcassi still mark the Roman Forum Cassii. The site was depopulated in the later Empire, when a smaller population retreated to the present strategic position commanding the valley, where it remained exposed to attack, in spite of the imposing walls that encircled it.