When the Fourth Crusade shattered the Byzantine Empire in 1204, the Frankish crusaders who swept into the Peloponnese did so with remarkable speed. By around 1209, the Principality of Achaea was established and its twelve secular baronies were being parceled out to the knights who had helped conquer the peninsula. Most of those baronies were created around 1209. Passavant, the twelfth and last, came later — shortly after 1218 or 1220 — because the territory it covered had not yet been fully conquered.

John de Nully was the man given the task. His father, Vilain of Nully, was a Norman from the village of Nully in France and a close friend of the historian Geoffrey of Villehardouin, whose chronicle of the Fourth Crusade is the primary source for these events. John himself did not take the cross — the crusading vow — until 1218, suggesting he arrived in the Peloponnese well after the first wave of Frankish settlement. His barony probably comprised newly conquered land at its edges, since Monemvasia, the last major Byzantine fortress in Laconia, did not fall until around 1248. The full pacification of the region was still two generations away when Passavant was established.

Four knights' fiefs made up the Barony of Passavant — a modest holding by the standards of the Principality of Achaea. But its strategic importance was outsized. The fortress sat at the geographical gateway between the Mani Peninsula and the rest of the Peloponnese, on the mountain ridge between the two. The Maniots — the inhabitants of the Mani — were famously resistant to outside authority. They built the tower houses that still define the Mani's visual character, fought their neighbors and each other across centuries, and maintained a culture of fierce independence that no medieval overlord fully domesticated.

To the east, on the slopes of Mount Taygetos, lived Slavic communities known to medieval sources as the Melingoi, who had settled in the mountains during earlier migrations and similarly chafed under Frankish administration. Watching over both groups required a position that commanded the approaches to the peninsula, which is precisely what Passavant provided. The military importance of the barony was recognized in a tangible way: John de Nully was named hereditary marshal of Achaea, the highest military office of the principality, an honor that passed through his line with the barony.

The historical record of Passavant is unusually thin. It was established in the early 1220s and conquered by the Byzantines of the Despotate of Epirus — later the Empire of Nicaea's successor state in the Morea — in the early 1260s. Between those two dates, virtually nothing is documented about the barony or its lords. The historian Karl Hopf, working in the 19th century, hypothesized that there had been two barons named John to account for the gap; the scholar Antoine Bon subsequently rejected that conjecture as unsupported by evidence.

What we are left with is a fortress on a mountain, a dynasty whose name appears and then vanishes, and a strategic position that clearly mattered to everyone who held it. The name Passava is still attached to the ruined castle in the hills above the Mani, visible to those who know where to look — a small fortress with a French battle cry in its name, watching a peninsula that was never entirely willing to be watched.

The Principality of Achaea reached its height in the mid-13th century, and Passavant fell during the period of Byzantine recovery that followed. After the Battle of Pelagonia in 1259, the Byzantines — specifically the Empire of Nicaea, which recaptured Constantinople in 1261 — pressed their advantage in the Peloponnese. The early 1260s saw a series of Byzantine gains in Laconia, and Passavant was among the baronies lost in this period.

With the Byzantine reconquest, Passavant ceased to exist as a Frankish institution. The fortress remained, as fortresses tend to do, used by whoever controlled the surrounding territory. The Principality of Achaea contracted but survived for another century and a half before finally dissolving in the early 15th century. Passavant, the last barony formed and one of the first lost, had lasted perhaps forty years as a Frankish outpost on the edge of the Mani — barely long enough to have a history, but long enough to leave a name on a ruined castle in the mountains above one of the most ancient and uncompromising landscapes in Greece.