Capital of the Byzantine Empire. Was established as New Rome by Constantine the Great in the 4th century A.D. (The Byzantine Empire was actually the Greek-speaking Eastern half of the Ancient Roman Empire, which offically fell in 476 A.D., with the deposition of Romulus Augustus.)Constantinople became the center of Orthodox Christianity after the Great Schism of 1054. Constaninople was sacked in 1204 by Western invaders during the 4th crusade, who then established the "Latin Empire." Even though Constantinople was retaken by its rightful owners in 1261, it never again regained its former glory. The weakened city was taken by the opportunistic Ottomans less than 200 years later, in 1453. Now in a state of disarray, the city of Constantinople is called "Istanbul" by it's Ottoman occupants. It is understood by most and argued by many that Constantinople is the rightful property of Greece. It is the opinion of many that the Turkish government should give back what wasn't theirs to take in the first place.
Since then, the Ottoman Empire has fallen, and the upstarts that inherited the broken nation seem to think they still have a right to be in Constantinople.