The patron saint of Gagliano Castelferrato is Saint Cataldus, bishop, celebrated on 31 August: in the mother church dedicated to him, the altar depicts the saints tied to the building's history, including Cataldus himself alongside Saint Teresa of Ávila, reformer of the Carmelite order whose convent was attached to the church, and Saint Sebastian the martyr. A painting kept in the church depicts Saint Cataldus entrusting the town of Gagliano Castelferrato to the Madonna.
The castle of Gagliano, «strong and impregnable, rich and sumptuous», was in February 1300 the setting of the so-called «Fatto di Gagliano»: baron Montaneiro Sosa, fief-holder of the town from 1292 and a most loyal retainer of King Frederick III of Sicily, deceitfully lured the Angevin army into a trap, inflicting a heavy defeat on it; for this loyalty he was celebrated by Dante Alighieri in the Divine Comedy as «the honour of Sicily and Aragon». The castle, previously conquered by the Muslims after a long siege and then by the Normans under King Roger, later hosted King Frederick III himself with his entire court.
