Borgo San Siro is an integral part of the monastery of San Salvatore of Pavia. It was mentioned in 1250 in the list of lands under the dominion of Pavia, as Burgum S. Syri. Like the nearby village of Tromello, in the following century it was taken over by the Beccaria family. Their lordship ended in 1475 with the death of Agostino Beccaria who was without heirs.