A Byzantine principality comprising the territories centred on Nicaea (now Iznik, Turkey). The Nicaean empire was established by Theodore I (1175–1222) following the sack of Constantinople during the Fourth Crusade; it adopted the institutions of the Byzantine empire, including emperors and patriarchs. Resisting the pressures of Seljuks and Crusaders, Theodore I successfully annexed lands from the Komnenoi of Trebizond. His son-in-law John III sustained this miniature empire in exile but the early death of his son, Theodore II (1254–58), enabled Michael VIII to dispossess and subsequently blind and imprison the infant heir, John IV Lascaris, after retaking Constantinople in 1261.