The gateway called Porta dell’Arce is located at the highest and most northerly point of the boundary walls, and it was even assumed that it could have been part of previous republican walls, of which no traces remain. Due to its proximity to the Capuchin monastery, it is also called Porta dei Cappuccini and through it, access was provided to the mountain.
It is composed of a single arch with a width of 3 metres and only the double arch of ashlars is preserved. The slit which housed the closing shutter is still visible, as are the abutments, although mostly buried. The outer side of the arch has a frame carved into the ashlars, which was probably also on the opposite side, but no traces remain. The arch is made of quadrangular blocks of dry white local stone.