In 1443, King Alfonso of Naples made Sora the seat of an independent Duchy; it was afterwards seized by Pope Pius II, but being restored to the Cantelmi by Pope Sixtus IV, it ultimately passed to the duke Giovanni Della Rovere. Against Cesare Borgia, the city was heroically defended by Francesco Maria I Della Rovere. It was purchased by Pope Gregory XIII for 11,000 ducats and bestowed under the suzerainty of Gregory's son, Giacomo Boncompagni (who was the first duke of Sora of the family).