The Church of St. Augustine in Castiglion Fiorentino took its name from 1333, when Augustinian friars settled in an earlier 13th-century building dedicated to St. Paul the Hermit in order to build a convent. In 1454 the church was connected to the square below by a monumental flight of steps, and in 1588, the square tower bell tower ending in a brick spire was built. The sandstone facade with a gabled roof was plastered in 1813.
Important peculiarity of the church, is the fact that it is one of the very few Italian churches to have had a large fresco on the exterior facade, representing three saints. The colors did not last long and the facade has now regained its original appearance.
The interior has a single nave and closes with three apsidal chapels. Among the works inside: a Madonna del Latte, a 14th-century fresco; a stone altar (1614) by Filippo Berrettini; the Annunciation by Niccolò Ghiori and the Madonna in Glory and Saints (1667) by Adriano Zabarelli. Originally kept in the church and now in the local art gallery are works by Florentine painter Jacopo del Sellaio. The walnut choir was carved by the Florentine Francesco Orlandi in 1750.
Next to the church remain the ruins of the monastic structures: the cloisters, one of which served as a cemetery, the chapter house, the refectory, and, on the upper floor, the monks' dwellings.