For 40 days in 1223, Francis withdrew to fast on the holm oak-covered slopes of Mount Rainero, the ‘Franciscan Sinai’. This was where the saint drew up the Rule of the Order. In front of the church is a portico rebuilt in 1940 and an adjoining convent, partly dating from the 15th century.
To the left of the church, a steep flight of steps leads to the Sacro Speco, the cave where Francis would retreat for meditation and where, it is said, a year before his death in 1225, he underwent an operation on his eyes for a serious illness he had perhaps contracted in the Holy Land. Before the descent, there is a tiny oratory with 13th-century frescoes in which the figure of Mary Magdalene, patroness of penitents, can be recognised.
The sanctuary of Fonte Colombo is one of the four Franciscan sanctuaries along the Way of Francis in the Holy Valley of Rieti, together with the convent of Greccio, the sanctuary of La Foresta, and the sanctuary of Poggio Bustone.