At the foot of Mount Pirchiriano, dominated by the Sacra di San Michele, and at the narrowest point between the hills and the valley floor, lies Chiusa San Michele, which owes its name to the characteristic geomorphology of the landscape. It was here in 773 that Charlemagne's Franks defeated Desiderius' Lombards, paving the way for the conquest of Italy.
Identifying the fortified system of the Lombard locks is complex, and recent archaeological excavations of the chapel of San Giuseppe have revealed masonry grafted onto the southern side of the ancient monument, which can probably be identified as the portion of the defensive wall connected to the fortification.
The original structure of the building seems to have been maintained and used over the centuries until its transformation into a church in the 18th century. The village of Chiusa winds along the ancient road to France, or Via Francigena, which runs along the right bank of the Dora to Bussoleno, and whose oldest part, known as the Rustico, unfolds through alleys and courtyards to the parish church of San Pietro Apostolo, built between 1796 and 1825. the interior, frescoed by Luigi Morgari, features a refined wooden choir in the presbytery attributed to Giuseppe Antonio Riva. The chapel of San Giuseppe now houses the Planetarium.