At the beginning of the siege, Mehmed sent out some of his best troops to reduce the remaining Byzantine strongholds outside the city of Constantinople.
The fortress of Therapia on the Bosphorus and a smaller castle at the village of Studius near the Sea of Marmara were taken within a few days.
The Princes' Islands in the Sea of Marmara were taken by Admiral Baltoghlu's fleet.
Mehmed's massive cannon fired on the walls for weeks, but due to its imprecision and extremely slow rate of reloading, the Byzantines were able to repair most of the damage after each shot, mitigating the cannon's effect.

Meanwhile, despite some probing attacks, the Ottoman fleet under Baltoghlu could not enter the Golden Horn due to the chain the Byzantines had previously stretched across the entrance.
Although one of the fleet's main tasks was to prevent any foreign ships from entering the Golden Horn, on 20 April, a small flotilla of four Christian ships managed to slip in after some heavy fighting, an event which strengthened the morale of the defenders and caused embarrassment to the Sultan.
Baltoghlu's life was spared after his subordinates testified to his bravery during the conflict.

Mehmed ordered the construction of a road of greased logs across Galata on the north side of the Golden Horn, and dragged his ships over the hill, directly into the Golden Horn on 22 April, bypassing the chain barrier.
This action seriously threatened the flow of supplies from Genoese ships from the nominally neutral colony of Pera, and it demoralized the Byzantine defenders.
On the night of 28 April, an attempt was made to destroy the Ottoman ships already in the Golden Horn using fire ships, but the Ottomans forced the Christians to retreat with heavy losses.
40 Italians escaped their sinking ships and swam to the northern shore.
 On orders of Mehmed, they were impaled on stakes, in sight of the city's defenders on the sea walls across the Golden Horn.
In retaliation, the defenders brought their Ottoman prisoners, 260 in all, to the walls, where they were executed, one by one, before the eyes of the Ottomans.
With the failure of their attack on the Ottoman vessels, the defenders were forced to disperse part of their forces to defend the sea walls along the Golden Horn.

The Ottoman army had made several frontal assaults on the land wall of Constantinople, but they were always repelled with heavy losses.
Venetian surgeon Niccolò Barbaro, describing in his diary one such land attack by the Janissaries, wrote:
They found the Turks coming right up under the walls and seeking battle, particularly the Janissaries ... and when one or two of them were killed, at once more Turks came and took away the dead ones ... without caring how near they came to the city walls.
Our men shot at them with guns and crossbows, aiming at the Turk who was carrying away his dead countryman, and both of them would fall to the ground dead, and then there came other Turks and took them away, none fearing death, but being willing to let ten of themselves be killed rather than suffer the shame of leaving a single Turkish corpse by the walls.

After these inconclusive frontal offensives, the Ottomans sought to break through the walls by constructing tunnels in an effort to mine them from mid-May to 25 May. Many of the sappers were miners of Serbian origin sent from Novo Brdo and were under the command of Zagan Pasha.
However, an engineer named Johannes Grant, a German who came with the Genoese contingent, had counter-mines dug, allowing Byzantine troops to enter the mines and kill the workers.
The Byzantines intercepted the first tunnel on the night of 16 May. Subsequent tunnels were interrupted on 21, 23, and 25 May, and destroyed with Greek fire and vigorous combat.
On 23 May, the Byzantines captured and tortured two Turkish officers, who revealed the location of all the Turkish tunnels, which were subsequently destroyed.

On 21 May, Mehmed sent an ambassador to Constantinople and offered to lift the siege if they gave him the city.
He promised he would allow the Emperor and any other inhabit
At the beginning of the siege, Mehmed sent out some of his best troops to reduce the remaining Byzantine strongholds outside the city of Constantinople. The fortress of Therapia on the Bosphorus and a smaller castle at the village of Studius near the Sea of Marmara were taken within a few days. The Princes' Islands in the Sea of Marmara were taken by Admiral Baltoghlu's fleet. Mehmed's massive cannon fired on the walls for weeks, but due to its imprecision and extremely slow rate of reloading, the Byzantines were able to repair most of the damage after each shot, mitigating the cannon's effect.
Meanwhile, despite some probing attacks, the Ottoman fleet under Baltoghlu could not enter the Golden Horn due to the chain the Byzantines had previously stretched across the entrance. Although one of the fleet's main tasks was to prevent any foreign ships from entering the Golden Horn, on 20 April, a small flotilla of four Christian ships managed to slip in after some heavy fighting, an event which strengthened the morale of the defenders and caused embarrassment to the Sultan. Baltoghlu's life was spared after his subordinates testified to his bravery during the conflict.
Mehmed ordered the construction of a road of greased logs across Galata on the north side of the Golden Horn, and dragged his ships over the hill, directly into the Golden Horn on 22 April, bypassing the chain barrier. This action seriously threatened the flow of supplies from Genoese ships from the nominally neutral colony of Pera, and it demoralized the Byzantine defenders. On the night of 28 April, an attempt was made to destroy the Ottoman ships already in the Golden Horn using fire ships, but the Ottomans forced the Christians to retreat with heavy losses. 40 Italians escaped their sinking ships and swam to the northern shore.  On orders of Mehmed, they were impaled on stakes, in sight of the city's defenders on the sea walls across the Golden Horn. In retaliation, the defenders brought their Ottoman prisoners, 260 in all, to the walls, where they were executed, one by one, before the eyes of the Ottomans. With the failure of their attack on the Ottoman vessels, the defenders were forced to disperse part of their forces to defend the sea walls along the Golden Horn.
The Ottoman army had made several frontal assaults on the land wall of Constantinople, but they were always repelled with heavy losses. Venetian surgeon Niccolò Barbaro, describing in his diary one such land attack by the Janissaries, wrote:
They found the Turks coming right up under the walls and seeking battle, particularly the Janissaries ... and when one or two of them were killed, at once more Turks came and took away the dead ones ... without caring how near they came to the city walls. Our men shot at them with guns and crossbows, aiming at the Turk who was carrying away his dead countryman, and both of them would fall to the ground dead, and then there came other Turks and took them away, none fearing death, but being willing to let ten of themselves be killed rather than suffer the shame of leaving a single Turkish corpse by the walls.
After these inconclusive frontal offensives, the Ottomans sought to break through the walls by constructing tunnels in an effort to mine them from mid-May to 25 May. Many of the sappers were miners of Serbian origin sent from Novo Brdo and were under the command of Zagan Pasha. However, an engineer named Johannes Grant, a German who came with the Genoese contingent, had counter-mines dug, allowing Byzantine troops to enter the mines and kill the workers. The Byzantines intercepted the first tunnel on the night of 16 May. Subsequent tunnels were interrupted on 21, 23, and 25 May, and destroyed with Greek fire and vigorous combat. On 23 May, the Byzantines captured and tortured two Turkish officers, who revealed the location of all the Turkish tunnels, which were subsequently destroyed.
On 21 May, Mehmed sent an ambassador to Constantinople and offered to lift the siege if they gave him the city. He promised he would allow the Emperor and any other inhabit
Fall of Constantinople