The founding of the abbey of S. Salvatore all’Isola, which goes back to 1001, is owed to Ava, a noblewoman of the Lambardi di Staggia family. The place where the monastery stands - which, as its name suggests, was once surrounded by water - was chosen mainly for its strategic position controlling the Via Francigena, of which Borgonuovo (subsequently Abbadia Isola) already constituted a resting place at the end of the 10th century.
Over the following centuries, one of the main functions of the abbey continued to be that of a hospital or a place of respite and hospitality for travellers on their way to Rome. After its foundation, the monastery experienced considerable economic and political success which continued through to the mid thirteenth century. Subsequently, in 1446, a slow decline began which led to the aggregation of the monastery with that of S. Eugenio near Siena.
Located on the edge of an extensive plain below the wooded slopes of Mount Maggio, the buildings are dominated by the Romanesque church with three naves and three apses. It is closely surrounded by a small hamlet and the remains of a medieval fortification. Inside the church are precious works of art, amongst which the beautiful polyptych over the main altar, created in the fifteenth century by the Siena born artist Sano di Pietro, is of particular note. To the right of the religious building there are still noticeable remnants of the bell tower and the monastery rooms, set out around the quadrangle of the ancient cloisters. Used for a long time as farm buildings, these are currently being restored and, in the future, will host guestrooms and a document centre for the Via Francigena.