Pope Gregory XII
In 1403, at the death of his father Antonio, Guidantonio inherited the family lands in the region of Italy called the Marche. Later he abandoned the Papal suzerainty and allied with King Ladislaus of Naples, who made him "Gran conestabile" of the Kingdom of Naples in 1411. Excommunicated by Pope Gregory XII, he took advantage of that move to conquer Assisi. He also controlled Castello, Cagli, Forlì, and Forlimpopoli.