The iuxta flumen Mellinum church has been documented from as long ago as 956 as belonging to the Abbey of St. Michele Arcangelo and listed in the bull of Pope Lucio III, issued in 1182 with the title of Sanctus Flavianus.

The monastery of the Poor Clares in Campomoro is mentioned for the first time in 1289, in the bull of Pope Niccolò IV, Cardinal Girolamo Masci from Ascoli, Franciscans of the Order of Friars Minor. In 1555, anticipating the Tridentine decrees, the nuns decided to abandon the ancient headquarters to move to the intra mœnia one, near the conventual complex of St. Francesco. Here they remained until the post-unification suppression, finding the definitive seat at the monastery dedicated to St. Fabiano and Sebastiano in via Garibaldi.