Constantinople
Constantinople (; ) was the capital city of the Roman/Byzantine Empire (330–1204 and 1261–1453), and also of the brief Crusader state known as the Latin Empire (1204–1261), until finally falling to the Ottoman Empire (1453–1923). It was reinaugurated in 324 from ancient Byzantium as the new capital of the Roman Empire by Emperor Constantine the Great, after whom it was named, and dedicated on 11 May 330. The city was located in what is now the European side and the core of modern Istanbul.
Third Rome
After the fall of Constantinople in 1453 AD, Mehmed II declared himself "Kayser-i Rum", literally "Caesar of Rome". The claim was recognized by the Orthodox Patriarch of Constantinople, but not by Roman Catholic Western Europe. Gennadios (Georgios Scholarios), a staunch enemy of the West, had been enthroned Patriarch of Constantinople with all the ceremonial attributes of Byzantium by Mehmed himself acting as Roman Emperor and in turn Gennadios recognized Mehmed as successor to the throne. Mehmed's claim rested with the concept that Constantinople was the seat of the Roman Empire, after the transfer of its capital to Constantinople in 330 AD and the fall of the Western Roman Empire. Mehmed also had a blood lineage to the Byzantine Imperial family; his predecessor, Sultan Orhan I had married a Byzantine princess, and Mehmed may have claimed descent from John Tzelepes Komnenos. During that period the Ottoman Empire also destroyed Otranto and its people, and Mehmed II was planning on taking Rome itself when the Italian campaign was cut short by his sudden death. The title fell into disuse after his death, but the imperial bodies created by Mehmed II lived on for centuries to come.