A great historic city, port, and the former capital (until 1923) of Turkey, situated on the Bosporus and partly in Europe, partly in Asia. Istanbul was founded c.660 bc by Dorian Greeks. Known as Byzantium until it became the second capital of the Roman Empire, it was renamed Constantinople in 330 ad by Constantine I. It was designed as a new Rome, straddling seven hills and divided into 14 districts. It was ruled by two emperors, until it was declared capital of the Eastern Roman Empire in 395. The city was largely rebuilt by Justinian (527–65). The capital of the Byzantine empire, the city withstood siege by Goths, Persians, and Arabs but was looted after a horrifying attack by Western Crusaders in 1204. It finally fell to the Ottoman Turks in 1453 and became the capital of the Ottoman empire. Most of its characteristic buildings, such as the Topkapi Palace, the Blue Mosque, and the Mosque of Suleiman the Magnificent, date from the Ottoman period (1453–1923).