What is the capital of istanbul?

With the fall of Rome and the Western Roman Empire, the name of the city was changed to Constantinople and became the sole capital of what historians now call the Byzantine Empire. This empire was distinctly Greek in culture, and became the centre of Greek Orthodox Christianity after an earlier split with Rome, and was adorned with many magnificent churches, including Hagia Sophia, once the world's largest cathedral. The seat of the Patriarch of Constantinople, spiritual leader of the Eastern Orthodox Church, remains.