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 oath s of fealty , they did so and were imprisoned by the Achaean prince . The triarchs ' wives , accompanied by many knight s 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 .