The Fourth Crusade forced AlexiosIII to flee from Constantinople in 1203. Theodore was imprisoned by the crusaders (commonly referred to as "Latins" by the Byzantines), but he escaped. After crossing the Bosporus into Asia Minor (in present-day Turkey), he started to organise the local Greeks' resistance against the Latins in Bithynia in his father-in-law's name. He concluded an alliance with the Seljuq Sultan of Rum, but he could not stop the Latins' expansion. Neither could he prevent a claimant to the imperial throne, Alexios Komnenos, from establishing a Byzantine successor state, the Empire of Trebizond, in northern Asia Minor. Theodore's position consolidated only after Tzar Kaloyan of Bulgaria inflicted a crushing defeat on the Latins in the Battle of Adrianople (in Thrace) in 1205.