The travertine spur on which the city was built and stratified from the pre-Roman era to the early Middle Ages after the III century BC, was circumscribed by a solid system of fortification in opus quadratum intercalated by the gates that circumscribed the urban stretch of the Salaria Road, the one that, through the centre of Italy, ensured the connection between the Tyrrhenian and the Adriatic seas, and represented the cardus and the decumanus of the city.

The Salaria crossed the Roman gate from south, at that time located in the highest part of the cardus, as the C. Carantio inscription on the façade of the church of St. Pietro Apostolo still remembers today. Then, it proceeded eastwards through the Herculana gate, while the decumanus continued westwards through the Quintia or Cinzia gate through a side road that looked towards Umbria.