- April 2: The army of Mehmet II sets up camp outside Constantinople. The siege of the city begins.
- April 18: Byzantines repel a Turkish night attack during the siege Constantinople.
- April 20: Four Byzantine ships break through the Ottoman fleet to supply besieged Constantinople.
- April 22: Turkish ships enter the Golden Horn over land to tighten the noose on besieged Constantinople.
- May 7: Byzantines repel another attack by the army of Mehmet II during the siege of Constantinople.
- May 22: A lunar eclipse occurs while Constantinople is under siege by the Ottoman Turks. The Byzantines take it as a bad omen since an old legend stated that Constantinople would never fall while the Moon was waxing in the sky.
- May 28: Emperor Constantine XI Palaeologus and much of the population of Constantinople attend the last services held at Hagia Sophia.
- May 29: The Fall of Constantinople to the Ottoman Turks.