Qaisar is the Arabic version of the name Caesar and it is used as a given name in Arabia. The Roman and later Byzantine emperors were called Qaisar-e-Rum (Caesar of Rome) by the Arabs and Persians. The Ottoman Sultans also took the title Qaisar-e-Rum (Caesar of Rome, meaning the Byzantine Empire) after conquering Constantinople, modern Istanbul, on May 29, 1453.