San Giorgio is a church built with donations from the Battle of Montaperti. Soldiers in the Sienese army used part of their pay to found the church for they had called on Saint George for help as their battle-cry during the battle.

Of the medieval edifice only the Romanesque-Gothic bell tower remains today. The current appearance dates to the intervention of Pietro Cremoni, who finished its reconstruction in 1738.

The façade is characterized by two giant columns and the coat of arms of Cardinal Anton Felice Zondadari, patron of the restoration. In the interior, on the counterfaçade, is the polychrome funerary monument to the painter Francesco Vanni (1656). Vanni himself provided the canvas with the Crucifixion with Father Matteo Guerra,  while an Encounter of the Lord with his Mother on the Calvary is by his son, Raffaello Vanni. The transept houses the tombs of two member of the Zondadari family.