It was founded as a Roman colony in the early 2nd century BC as a defensive outpost on the Mincio crossing along the Via Postumia from Cremona to Verona.
123 BC - 118 BC at the junction of the great roads; the Via Postumia and the Via Aemilia Scauri which merged to become the Via Julia Augusta.
From Cremona the road ran eastward to Bedriacum, the current town of Calvatone, where it forked, one branch running to the right to Mantua, the other to the left to Verona, crossing the Adige river on the Ponte Pietra, the only bridge on the Adige river at that time, and ending at Aquileia, important military frontier town since Republican times.
Clastidium (modern Casteggio), was a village of the Anamares, in Gallia Cispadana, on the Via Postumia, 5 miles east of Iria (modern Voghera) and 31 miles west of Placentia.