The church, built in the last decade of the 14th century, was often used as a hall for the Council during the periods of war and the plague. The church and convent were soon given over to the Augustine Order which took up residence in the Municipal building at the end of the 15th century. They enlarged the nearby convent through restorations and extensions. In this sacred place, the Venerable Giovanni Nicolucci took his vows and became rector, taking on the name of Father John of San Guglielmo, known as the Apostle of the Maremma. He lived and worked during the period of the Grand Dukes of Tuscany, Ferdinand and Cosmos II. The interior of the church is a splendid example of a three-nave Marche Baroque style.