William II of Villehardouin William II of Villehardouin , ( Guillaume II de Villehardouin ) ( died May 1 , 1278 ) was the last Villehardouin prince of Achaea and ruled the principality at the height of its power and influence . William was the son of Geoffrey I Villehardouin . In 1236 he aided the Latin Empire against the Byzantine Empire of Nicaea , and was rewarded with the overlordship of the Venetian Duchy of the Archipelago and other Venetian territories in the Aegean Sea . In 1239 he married the daughter of Narjot de Toucy and of Narjot ' s first wife ( who was the daughter of the dowager empress Anna ) . William came to power in Achaea in 1246 when his brother Geoffrey II Villehardouin died . As prince he conquered the remaining territory of the Peloponnese ( known at the time as Morea ) and built the fortress of Mistra near Sparta . In 1249 he captured Monemvasia with help from his Euboeote vassals , and later that year accompanied Louis IX of France on the Seventh Crusade , joining him in Cyprus with 400 knights and 28 ships . Louis also gave him a license to mint coins in the style of royal French money . Under William ' s rule the Duchy of the Archipelago , the Duchy of Athens , and the Lombard lords ( " triarchs " ) of Euboea recognized him as their lord . In 1255 his Venetian second wife Carintana dalle Carceri died , leading to a dispute over the inheritance of a fief in Euboea , and war broke out between Venice and Achaea ( the " War of the Euboeote Succession " " terciers " being the three Lombard lords of the island ) . William won the war and also defeated the Duke of Athens in 1258 , reaffirming his influence over the duchy . In 1259 he married Anna Komnene Doukaina , daughter of Michael II of Epirus , forming an alliance with the Byzantine Despotate of Epirus against Nicaea , an alliance which also included Manfred of Sicily . In September of that year he led the Achaean forces at the Battle of Pelagonia against the Nicaeans , but the Epirote army deserted and William was defeated . He fled the field and hid under a haystack , where he was captured and brought to Nicaea . He remained in captivity until 1262 , and was forced to hand over Grand Maigne , Monemvasia and Mistra to the Byzantine Empire , which had been restored in Constantinople the previous year . William had now lost all of his previous power , as had his former lord , Baldwin II of Constantinople , whose Latin Empire was lost with the Byzantine restoration . William and Baldwin both acknowledged Charles of Anjou as lord of Achaea under the Treaty of Viterbo in 1267 ; Charles had earlier defeated and killed William ' s old ally Manfred . As a vassal of Charles , William and 400 Achaean knights fought against Conradin at the Battle of Tagliacozzo in 1268 . William and Anna had two daughters , Isabella and Margaret ; Isabella , the elder daughter , married Charles ' s son Philip of Sicily , who , however , predeceased his father . Charles personally succeeded William in 1278 , ending the Villehardouin dynasty and setting up Angevin rule , with the principality governed essentially as a province of the Kingdom of Naples . With the decreasing power and influence of Achaea , the Duchy of Athens became the most powerful state in Greece . William was also noted as a poet and troubadour , and the " Manuscrit du Roi " , containing two of his own compositions , was written in Achaea during his reign . He was fluent in both French and Greek .