Familiarity with the Slavic element in the area led two brothers from Thessaloniki, Saints Cyril and Methodius, to be chosen to convert the Slavs to Christianity. Following the campaigns of Basil II, all of Macedonia returned to the Byzantine state. Following the Fourth Crusade 1203–1204, a short-lived Crusader realm, the Kingdom of Thessalonica, was established in the region. It was subdued by the co-founder of the Greek Despotate of Epirus, Theodore Komnenos Doukas in 1224, when Greek Macedonia and the city of Thessaloniki were at the heart of the short-lived Empire of Thessalonica. Returning to the restored Byzantine Empire shortly thereafter, Greek Macedonia remained in Byzantine hands until the 1340s, when all of Macedonia (except Thessaloniki, and possibly Veria) was conquered by the Serbian ruler Stefan Dušan. After the Battle of Maritsa (1371), Byzantine rule was reestablished in eastern regions, including Serres. During the 1380s, the region was gradually conquered by the advancing Ottomans, with Serres holding out until 1383, and Thessaloniki until 1387. After a brief Byzantine interval in 1403–1430 (during the last seven years of which the city was handed over to the Venetians), Thessaloniki and its immediate surrounding area returned to the Ottomans.