The Porta Praetoria is the most complete Roman gate in the Alpine region, and one of the best-preserved anywhere in Italy. Built in the final decades of the first century BC, it consists of two parallel arched facades — an outer gate and an inner gate — with a rectangular courtyard between them. The outer arch was flanked by towers of which substantial remains survive. The whole structure served both as a fortified entrance and as an architectural statement: this was a Roman city, and it looked like one.
The gate faces east along what is now Via Sant'Anselmo, the main pedestrianised street through the old town. Standing beneath the inner arch and looking back through the outer one gives a direct view out to the mountains framing the valley. The stonework is local granite, cut and fitted without mortar in the Roman fashion, and the precision of the joints is still visible. At street level, a small medieval chapel was later built into the fabric of the gate on the north side — a reminder that after the Romans departed, the structure became a fortified strongpoint in a long succession of medieval conflicts.