Under his son and successor, Prince William II Villehardouin, the Principality reached its zenith. William was a poet and troubadour, and his court had its own mint at Glarentza, and a flourishing literary culture, using a distinct form of spoken French. In 1249, William II moved the capital of Achaea to the newly built fortress of Mistra, near ancient Sparta. In 1255 he became embroiled in the War of the Euboeote Succession, and in 1259 he allied with Michael II, despot of Epirus, against Michael VIII Palaeologus of Nicaea. However, Michael II then deserted to join the Nicaean side, and William was taken prisoner at the Battle of Pelagonia. After Michael recaptured Constantinople in 1261, William was released in 1262 in return for Mistra and much of Laconia, which became a Byzantine province (the nucleus of the future Despotate of the Morea), as well as an oath of allegiance to the Emperor.