The Byzantine Emperor Manuel II Palaiologos supported Süleyman as claimant to the Ottoman throne. They signed the treaty of Gallipoli with the Byzantine regent John VII Palaiologos in 1403, as the emperor Manuel II Palaiologos was traveling in western Europe at the time. By this treaty, Süleyman gave up certain territories along the Marmara coast, as well as the major city of Thessaloniki to the Byzantine Empire in return for Byzantine support during the interregnum and declared himself sultan of the empire in Edirne, the capital in Rumeli of the Ottoman Empire.