The Fourth Crusade
The 13th century began with what is generally considered to be the final sealing of the schism between East and West, when the knights of the Fourth Crusade brutally sacked Constantinople during the first three days of Holy Week in 1204. They pillaged Hagia Sophia and other churches, desecrating the altars and stealing countless relics and other holy objects. The Crusaders took control of the city. A Latin, Thomas Morosini, was named Patriarch of Constantinople; and a Frank, Baldwin of Flanders, was named “Emperor of Byzantium.” Now, for the first time, the entire Latin West became a deeply hated enemy in the minds of the Greek people.
Most of the Byzantines regrouped in northwestern Asia Minor, in what they called the Empire of Nicea. They were led by the capable new Emperor Theodore I Laskaris (r. 1204–1222), who was succeeded by his saintly son-in-law, Emperor Saint John III Doukas Vatatzes (r. 1222–1254). By 1261, Emperor Michael VIII Paleologos (r. 1259–1282) was able to regain Constantinople from the Latins. Even though the Byzantine Empire lasted for almost another 200 years, she never fully recovered from the devastation of the Fourth Crusade and the 57 years of Latin rule in her capital city.