Pope Gregory IX placed the first stone of the Lower Basilica the day after the canonization of the Saint in July 1228. Two years later, the Saint's body was transported and buried in secret in the Unfinished Church.
The beginning of works for the Upper Church is not passed down, however, should be around 1239.
In 1754 the church was elevated to the rank of Basilica. Because of the little space on the hill chosen for the complex, were necessary the majestic walls supporting structure for the convent building and the papal palace.
Inside, are the famous frescoes of the school of Cimabue and Giotto.