There are tall Gothic windows with Geometric tracery in each bay of the nave and in the polygonal apse of the chancel. The windows of the apse are believed to have been created by German craftsmen active around Assisi at the end of the 13th century. The windows on the left hand side of the nave were made by a French workshop (1270), while those on the right hand side are attributed to the workshop of Maestro di San Francesco. These stained glass windows are among the best examples of 13th-century Italian glasswork.