The County of Sora had been constituted in 1399 as a fief of the Kingdom of Naples. In 1443 Nicola Cantelmo, who was already count of Sora and nearby Alvito, was named the first duke of Sora by Alfonso I. His fief was intended as a buffer between the Neapolitan kingdom and the Papal States. The Cantelmi struggled in the 15th century for a greater degree of autonomy, often taking advantage of the succession crises that threatened to tear apart the Kingdom of Naples until the early 16th century. In 1450, during one of these wars, Pope Pius II, who supported the Aragonese party, sent Federico III da Montefeltro against the Cantelmi. The Soran army was defeated and the duchy pacified. In 1463 however the Cantelmi rebelled again. This time the papal commander was Napoleone Orsini, who captured Isola del Liri, Arpino, and a large piece of territory, making Sora a papal fief. Piergiampaolo Cantelmo lost the ducal title. His remaining lands in Alvito and Popoli were assigned to his brother Giovanni Cantelmo with the title of Count. In 1472 Pope Sixtus IV renounced his feudal rights over Sora: the duchy of Sora, now separated from that of Alvito and augmented by the addition of Arce, was given to his nephew Leonardo della Rovere, who married a daughter of King Ferdinand I of Naples.
In 1579 Pope Gregory XIII acquired the duchy for 100,000 scudi, assigning it to his son Giacomo Boncompagni. The duchy was also at this time enlarged by the acquisition of Aquino and Arpino, becoming a truly autonomous seigniory only nominally dependent on the Kingdom of Naples. The creation of an independent state in southern Lazio had been managed by cardinal Francesco Maria Del Monte to counterbalance the expansion of the House of Farnese. Giacomo married Costanza Sforza, who embellished the duchy with buildings, gardens and schools. The Dukes promoted local industry by installing textile factories in Arpino and Sora and a paper industry along the Liri River. They also founded a new town, Colle Drago, but after Giacomo and his successor Gregorio I, the financial difficulties of the family, caused by such expensive projects, prevented further efforts. At the death of duke Giovan Giacomo, his brother Ugo had to face the popular rebellion of the brigandPapone, a follower of the republicanism of Masaniello. He occupied Sora and Cassino and formed a popular government. Ugo was succeeded by his son Gregorio II, who married Ippolita Ludovisi, who added to his lands the principality of Piombino. The union of the Boncompagni and Ludovisi families as the Boncompagni-Ludovisi largely resolved their economical difficulties, but at that time the duchy was facing increased custom taxes imposed by the Papal States on its merchants. Gregorio II's successor, Antonio I, died in 1731, leaving his lands to his son Gaetano, who relaunched a policy of social and economical improvements in the Liri Valley, as well as the embellishment of Colle Drago. The last Duke was Antonio II, who ceded his state to King Ferdinand I of the Two Sicilies in 1796.
