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.