Constantinople was the capital of the Byzantine (Roman) Empire and, in the Middle Ages, the largest and wealthiest city in Europe. In 1930, Constantinople was changed to its modern day name of Istanbul. Istanbul is the largest city in Turkey. It was known by a few names for several centuries. The main secondary name being, Constantinople. In 1923, the Turkish government decided it was best for the city to only go by one name, and Istanbul was chosen. Istanbul is home to the world famous cathedral, the Hagia Sophia.