Independent principality (1204–61) of the fragmented Byzantine Empire. Founded in 1204 by Theodore I Lascaris, it was the political and cultural centre from which a restored Byzantium arose in the mid-13th century under Michael VIII Palaeologus. It extended from the Black Sea coast east of the Sangarius River southwest across western Anatolia to Miletus and the Menderes (Maeander) River. It became a centre of Greek education, especially under Theodore II Lascaris, who founded an imperial school. It declined after 1261, when Michael VIII regained the Byzantine capital of Constantinople.