Complex sentence: Zeno's successors ruled from Constantinople (modern Istanbul) until the conquest of that city by the Ottoman Turks in 1453, when the emperor Constantine XI died in hand to hand combat defending the capital.
Split into simpler sentences: Zeno's successors ruled from Constantinople (modern Istanbul) until the conquest of that city by the Ottoman Turks in 1453. The last Roman Emperor, Constantine XI died in hand to hand combat defending the capital.