Constantine the Great effectively became the emperor of the whole of the Roman Empire in September 324. Two months later, Constantine laid out the plans for a new, Christian city to replace Byzantium. As the eastern capital of the empire, the city was named Nea Roma; however, most simply called it Constantinople, a name that persisted into the 20th century. Six years later, on 11 May 330, Constantinople was proclaimed the capital of an empire that eventually became known as the Byzantine Empire or Eastern Roman Empire. The establishment of Constantinople served as one of Constantine’s most lasting accomplishments, shifting Roman power eastward as the city became a center of Greek culture and Christianity. The city subsequently became the center of the Latin Empire, created by Catholic crusaders to replace the Orthodox Byzantine Empire. Various economic and military policies instituted by Andronikos II, such as the reduction of military forces, weakened the empire and left it more vulnerable to attack. In the mid-14th century, the Ottoman Turks began a strategy of taking smaller towns and cities over time, cutting off Constantinople’s supply routes and strangling it slowly. Mehmed declared himself as the new Roman emperor and the Ottoman state was reorganized into an empire.
Today Istanbul is the largest city in Turkey, constituting the country’s economic, cultural, and historical heart with a population of 13.9 million.