Founded at the end of the 5th century, is in the middle of the town, and is rather lower than street level.
Over the centuries it underwent many modifcations and in the grounds surrounding it there a round 16th century bell-tower. The façade features a four sided portico with above it a beautiful marble two-light window.
The interior with a trussed ceiling has a nave and two aisles and contains Corinthian capitals of the 6th century. Very interesting are an ancient sarcophagus that contains the ashes of San Giorgio Martire and of the Archbishop Agnellus. The painting above the altar representing Sant'Agata is by Luca Longhi.