The Barony of Arcadia began as something of a political consolation. It was not among the original twelve secular baronies of the Principality of Achaea; it was created after the fact, for a displaced lord seeking refuge. Vilain of Aulnay died in 1269, and his sons Erard and Geoffrey split the inheritance. Things grew complicated almost immediately. Erard was captured by the Byzantines in 1279 and disappeared from the record. Geoffrey, meanwhile, could not reclaim his brother's half of the barony until 1293 — blocked for over a decade by the Angevin administrators who governed Achaea and who had sequestered the domain. The barony thus spent its first generation mired in the gap between what the law permitted and what the powerful would allow.

The story of the barony in the fourteenth century is one of fragmentation and attempted reunion, played out through a succession of marriages, deaths, and inheritance disputes that reads, at times, like something from a chronicle of misfortune. Erard II of Aulnay died before 1338, leaving his half of the barony apparently to his widow, Balzana Gozzadini, who married Peter dalle Carceri, Triarch of Negroponte — only for Balzana to die soon after. His sister Agnes had married Stephen Le Maure, known as "The Moor," Lord of Saint-Sauveur and Aetos, and their son Erard III eventually reunited the barony by 1344. He was named marshal of Achaea in 1345, a moment of restored prestige. Then, in 1348, a Burgundian knight named Louis of Chafor stormed the castle with a band of companions and held Erard's wife and children hostage until Erard paid a large ransom. The barony that had once been a diplomatic gift was now a prize worth seizing by force.

When Erard III died in 1388, the barony passed to one of his daughters, who married Andronikos Asanes Zaccaria, drawing the domain into the orbit of the powerful Zaccaria family — Genoese lords who had built influence across the Aegean. The Zaccaria claim was contested by Erard Laskaris, a grandson or nephew of Erard III, but he made no headway and died without children in 1409. The last baron of the Zaccaria line to hold Arcadia in any meaningful sense was Centurione II Zaccaria, who retained the barony as his personal fief even after the Principality of Achaea effectively collapsed — the Byzantine Despotate of the Morea having captured Patras and Chalandritsa in 1429–30. Arcadia was, in other words, the last piece of the old Frankish Principality still standing. When Centurione died in 1432, his son-in-law, the Byzantine Despot Thomas Palaiologos, annexed it and imprisoned Centurione's widow, who died in captivity. The barony that began as a consolation prize ended as the final ember of a two-century Frankish project on the Peloponnese.

Beneath the dynastic genealogy lies a real place: the coastal town of Kyparissia, perched between sea and hills on the western shore of Messenia. The Franks called it Arcadia — borrowing the name from a region in the interior of the Peloponnese and relocating its romantic connotations to this coastal settlement. The castle on the hill east of the town, which still stands in modified form today, was the seat of all those barons and their disputes. From its walls, one could see the Gulf of Kyparissia opening onto the Ionian Sea, and on clear days, the low shapes of the Strofades islands offshore. The town below was small but had been important since antiquity, when Homer mentioned it and the geographer Pausanias found temples to Apollo and Athena within its walls. What the Franks built on that rocky hill was layered onto millennia of prior occupation — a pattern that would repeat when the Byzantines took it back, and then the Ottomans after them.