War of the Euboeote Succession

The War of the Euboeote Succession was fought in 1256–1258 between the Prince of Achaea, William II of Villehardouin, and a broad coalition of other rulers from throughout Frankish Greece who felt threatened by William's aspirations. The war was sparked by William's attempt to gain control of a third of the island of Euboea, which was resisted by the local Lombard barons ("terciers" or "triarchs") with the aid of the Republic of Venice. The Lord of Athens and Thebes, Guy I de la Roche, also entered the war against William, along with other barons of Central Greece. Their defeat at the Battle of Karydi in May/June 1258 effectively brought the war to an end in an Achaean victory, although a definite peace treaty was not concluded until 1262.

Background
Following the Fourth Crusade, southern Greece had been divided among several Latin lordships, the most powerful of which was the Principality of Achaea, which controlled the entire Peloponnese peninsula. William II of Villehardouin, who in 1246 had succeeded his elder brother as prince, was a most energetic ruler, who aimed to expand and consolidate his rule over the other Latin states. Guy I de la Roche, the "Great Lord" of Athens and Thebes, was already his vassal for the fief of Argos and Nauplia, which lay in the Peloponnese, and William was also suzerain of the three Lombard baronies (terzieri, "thirds") of Negroponte (the medieval name of both the island of Euboea and its capital, modern Chalkis).

In 1255, William's second wife, Carintana dalle Carceri, baroness of the northern third of the island, died, and her husband laid claim to her inheritance, even minting coins presenting himself as "Triarch of Negroponte". The other two triarchs, however, Guglielmo I da Verona and Narzotto dalle Carceri, rejected his claim. Although they were William's nominal subjects and, in Guglielmo's case, even related to him by marriage, they were loath to surrender Euboeote territory to someone outside their own families. Instead, they ceded Carintana's barony to their kinsman, Grapella dalle Carceri. In this, they were supported by Paolo Gradenigo, the Venetian bailo (representative) at Chalkis, the capital of Euboea. Venice had a long presence at Chalkis, which was an important trading station, and exercised considerable influence over the island and the triarchs.

Contest for Chalkis
On 14 June 1256, a treaty was signed between the Lombard triarchs and Gradenigo on 14 June 1256. In exchange for the Venetian alliance against Achaea, the triarchs renewed their previous agreements, ceded possession of the fortress of Chalkis, which controlled the bridge over the Euripus Strait, and of extensive lands on the island. The triarchs and their domains were freed from any duties and the considerable tribute that they paid to Venice until then, but in turn, they gave up the rights to all customs revenue to the Republic. Venice also received further concessions, such as the right to regulate the weights, measures and scales for all Euboea, and privileges for its citizens. Soon after, according to the historian Marino Sanudo, William called upon Guglielmo and Narzotto to present themselves to him. Constrained by their feudal oaths of fealty, they did so and were imprisoned by the Achaean prince. The triarchs' wives, accompanied by many knights and other kinsmen, then went to Marco Gradenigo, the newly arrived bailo, and beseeched his aid. "Moved alike by policy and sympathy", as the historian William Miller states, Gradenigo assented.

William, moving quickly in support of his own claims, had already seized Chalkis. Gradenigo and his Venetians attacked and took the city, but William responded by sending his nephew the baron of Karytaina, Geoffroy de Bruyères, who recaptured Chalkis and launched devastating raids in Euboea. Venice then laid siege to the city, which dragged on for thirteen months until its defenders capitulated in early 1258. An Achaean counterattack was repulsed by Venetian infantry sallying forth and defeating the famed Achaean cavalry before the city's walls.

Anti-Achaean League and the Battle of Karydi
Faced with the opposition of Venice, William of Villehardouin turned to her rival, Genoa, for support. Based at Monemvasia, Genoese-crewed galleys preyed upon Venetian shipping. Othon de Cicon, the lord of Karystos in southern Euboea, in control of the strategic passage of the Cavo D'Oro, also sided with William. Elsewhere, however, William's appeals were met with hostility and mistrust, due to the Achaean ruler's claims of suzerainty over all the Latin princes of southern Greece. From the summer of 1256, Guy I de la Roche, the "Great Lord" ("Megaskyr") of Athens and Thebes, and his brother William, had joined the Venetian camp, although they were both vassals to the Villehardouins (Guy as Lord of Argos and Nauplia and his brother as baron of Veligosti and Damala): the treaty between Venice and the triarchs had been signed at Guy's capital, Thebes, while both Guy and William actively aided the Venetians in their siege of Chalkis. Thomas II de Stromoncourt, the Lord of Salona, and Ubertino Pallavicini, the Margrave of Bodonitsa, also entered in the anti-Achaean coalition, to be joined soon after by Geoffroy de Bruyères, who deserted his uncle's cause.

William of Villehardouin responded by launching a full-scale invasion of the de la Roche domains. His army crossed the Isthmus of Corinth, and at the pass of Mount Karydi, on the way from Megara to Thebes, his army decisively defeated the coalition army. Guy de la Roche and the other barons fled the field and found refuge in the citadel of Thebes. William of Villehardouin followed after them and prepared to lay siege to the city, but relented after the Latin archbishop and many of his own nobles pleaded to show restraint and end the conflict. After extracting a pledge by Guy de la Roche to appear before the Achaean High Court, the assembly of the Achaean barons, and be judged, William's troops withdrew.

The High Court quickly assembled at Nikli. Guy de la Roche presented himself before it accompanied by his own knights, but the assembled barons decided that they did not have the authority to judge him, and referred the matter to King Louis IX of France (r. 1226–1270). Guy travelled to France in 1259, but Louis not only pardoned him, but awarded him the title of Duke, which he was to bear thereafter. The renegade Geoffroy de Bruyères too was brought for judgment before William, and it was only the determined and passionate intercession of the other barons that saved his life and secured a pardon from the vengeful prince.

Aftermath
William's victory at Karydi, coupled with a victory of his troops against the Venetians near Oreoi, brought an effective end to the conflict; on 6 August 1258, Guglielmo da Verona and Narzotto dalle Carceri consented to begin negotiations for peace through the Doge of Venice, and in early 1259, the Doge authorized the new bailo, Andrea Barozzi, to sign a treaty with William. But due to William's subsequent involvement in the great Epirote-Achaean-Sicilian alliance against the Empire of Nicaea, his defeat and capture at the Battle of Pelagonia and his captivity at the hands of the Nicaean emperor Michael VIII Palaiologos (r. 1259–1261), a final peace treaty was delayed until William's release in 1262. The treaty, signed at the residence of the Archbishop of Thebes, essentially restored the status quo ante: William recognized Guglielmo, Narzotto, and Grapella as triarchs, and they in turn swore their allegiance to him. The fortress of Chalkis was razed, but Venice retained and even increased its quarter in the city, as well as retaining its exclusive right to levy customs in Euboea, except for the triarchs, the Prince, and their agents. Thus, Venice retained some of its 1256 gains, but overall the treaty was regarded as a setback, in view of the considerable expenses incurred. For some time afterwards, Venice was content to exercise her financial privileges, and refrained from meddling with the island's politics.