What was the city of Constantinople called before it became known as Constantinople?

Explanation

Istanbul is the largest city in Turkey. It is located on both banks of the Bosphorus strait. This means that the city lies both in Europe and in Asia (Anatolia). The city only gained its current name in 1931. Before that, it was called Constantinople and before that, Byzantium. The Turks captured Constantinople in 1453 and made the city the capital of the Ottoman Empire.