The tomb of Saint Francis is in the crypt in the lower church, Chiesa Inferiore. A Renaissance porch is in front of the 13th century entrance. There are frescoes and a Gothic style high altar.
The upper church, Chiesa Superiore, was built in the second part of the 13th century and has a Gothic facade with a large rose window with a smaller rose window above it. Frescoes by both Giotto and Cimabue are inside. The most famous is the cycle of the Life of Saint Francis. It was done by Giotto and his assistants from 1296-1300.
The Romanesque bell tower was constructed in 1239. Inside the museum, Museo Tesoro are paintings, gold craft, and textiles, some from the 13th century.