From the Porta Principalis Sinistra the itinerary that once led to the Gran San Bernardo Pass commenced (Summus Poeninus). Up until 1843, the remains of this building were still visible in the northern part of Roncas square; Palazzo Rolle, a building dating back to the 30’s, situated at the side of Palazzo Roncas, occupies the area of one of the towers (the western one) that flanked the Roman doorway.

The eastern tower, on the other hand, called “de la porte” during the middle ages, became the nucleus around which a feudal dwelling place rose up, the ancient bastion was demolished during the course of the 17th century, by which time it had become part of the Visitation convent. Its appearance is recognisable in a late-seventeenth century view of Aosta, while its presence is still certified in the map by De Tillier dated 1730.

In the basement area of the Regional Archaeological Museum (ex Visitation convent) you can observe the remains of the south-eastern edge of this tower, with the Roman use levels and the only section of embankment, with the relative counterscarp, still resting on a section of the roman walls.