The fall of Constantinople was when the Ottoman Empire took over Constantinople, the capital city of the Byzantine Empire, on 29 May 1453.
The Ottomans were commanded by 21-year-old Ottoman Sultan Mehmed II, who defeated an army commanded by Byzantine Emperor Constantine XI Palaiologos.
The conquest of Constantinople followed a 53-day siege started on 6 April 1453.

This event marks the end of the Byzantine Empire, and so it was the end of the Roman Empire, which had lasted for nearly 1,500 years.
Previous Sultans had taken most of the Empire in previous centuries.
Some places, like the Morea Despotate and Empire of Trebizond were not defeated by the Ottomans until several years later.

The fall of Constantinople had important results, because the Ottoman Turks at last had control of the Balkans.
Nothing could stop them from further Muslim conquests in Europe, which went on until after the Battle of Vienna in 1683.
After the fall of Constantinople and the Byzantine empire, many refugees escaped to Western Europe and helped create humanism.
In particular, the arrival in Italy of Greek scholars is said to have helped the Renaissance.
The fall of Constantinople was when the Ottoman Empire took over Constantinople, the capital city of the Byzantine Empire, on 29 May 1453. The Ottomans were commanded by 21-year-old Ottoman Sultan Mehmed II, who defeated an army commanded by Byzantine Emperor Constantine XI Palaiologos. The conquest of Constantinople followed a 53-day siege started on 6 April 1453.
This event marks the end of the Byzantine Empire, and so it was the end of the Roman Empire, which had lasted for nearly 1,500 years. Previous Sultans had taken most of the Empire in previous centuries. Some places, like the Morea Despotate and Empire of Trebizond were not defeated by the Ottomans until several years later.
The fall of Constantinople had important results, because the Ottoman Turks at last had control of the Balkans. Nothing could stop them from further Muslim conquests in Europe, which went on until after the Battle of Vienna in 1683. After the fall of Constantinople and the Byzantine empire, many refugees escaped to Western Europe and helped create humanism. In particular, the arrival in Italy of Greek scholars is said to have helped the Renaissance.
Fall of Constantinople