Erected between 1257 and 1265, on the site of the church of San Giorgio where St. Francis was buried. In Gothic style, according to the Franciscan model, it has a gabled façade, a nave, a polygonal apse and is divided into four bays. The plan is T-shaped, on axis with the door. There is a magnificent rose window. On the sides there are three large flying buttresses (1351), to support the thrust of the vaulted roof; those of the right side are hidden inside the monastery; others are projected on the square, giving it a distinctive appearance. The interior preserves the Crucifix which, according to tradition, spoke to St. Francis, has frescoes of the Umbrian school of the thirteenth and fourteenth centuries, and in the crypt is preserved a sarcophagus statue with the bones of the saint inside. Next to the church is the monumental Proto-Monastery of St. Clare (the cloister is not open to public), built in on a slope between Borgo Aretino and Mojano, among the olive groves. In the cloister the crypt of the ancient Church of San Giorgio can be seen.