Following the Mongols from Central Asia came the Ottoman Turks. By 1400 they had captured most of modern-day Turkey and extended their rule into Europe through the Balkans and as far as the Danube, surrounding even the fabled city of Constantinople. Finally, in 1453, one of Europe's greatest cities fell to the Turks. The Ottomans under the command of Sultan Mehmed II, fought a vastly outnumbered defending army commanded by Emperor Constantine XI — the last "Emperor of the Eastern Roman Empire" — and blasted down the ancient walls with the terrifying new weaponry of the cannon. The Ottoman conquests sent refugee Greek scholars westward, contributing to the revival of the West's knowledge of the learning of Classical Antiquity.