The city had about 20 km of walls (land walls: 5.5 km; sea walls along the Golden Horn: 7 km; sea walls along the Sea of Marmara: 7.5 km), one of the strongest sets of fortified walls in existence.
The walls had recently been repaired (under John VIII) and were in fairly good shape, giving the defenders sufficient reason to believe that they could hold out until help from the West arrived.
In addition, the defenders were relatively well-equipped with a fleet of 26 ships: 5 from Genoa, 5 from Venice, 3 from Venetian Crete, 1 from Ancona, 1 from Aragon, 1 from France, and about 10 from the empire itself.

On 5 April, the Sultan himself arrived with his last troops, and the defenders took up their positions.
As Byzantine numbers were insufficient to occupy the walls in their entirety, it had been decided that only the outer walls would be manned.
Constantine and his Greek troops guarded the Mesoteichion, the middle section of the land walls, where they were crossed by the river Lycus.
This section was considered the weakest spot in the walls and an attack was feared here most.
Giustiniani was stationed to the north of the emperor, at the Charisian Gate (Myriandrion); later during the siege, he was shifted to the Mesoteichion to join Constantine, leaving the Myriandrion to the charge of the Bocchiardi brothers.
Minotto and his Venetians were stationed in the Blachernae Palace, together with Teodoro Caristo, the Langasco brothers, and Archbishop Leonardo of Chios.

To the left of the emperor, further south, were the commanders Cataneo, who led Genoese troops, and Theophilus Palaeologus, who guarded the Pegae Gate with Greek soldiers.
The section of the land walls from the Pegae Gate to the Golden Gate (itself guarded by a Genoese called Manuel) was defended by the Venetian Filippo Contarini, while Demetrius Cantacuzenus had taken position on the southernmost part of the Theodosian wall.

The sea walls were manned more sparsely, with Jacobo Contarini at Stoudion, a makeshift defence force of Greek monks to his left hand, and Prince Orhan at the Harbour of Eleutherios.
Pere Julià was stationed at the Great Palace with Genoese and Catalan troops; Cardinal Isidore of Kiev guarded the tip of the peninsula near the boom.
Finally, the sea walls at the southern shore of the Golden Horn were defended by Venetian and Genoese sailors under Gabriele Trevisano.

Two tactical reserves were kept behind in the city: one in the Petra district just behind the land walls and one near the Church of the Holy Apostles, under the command of Loukas Notaras and Nicephorus Palaeologus, respectively.
The Venetian Alviso Diedo commanded the ships in the harbour.

Although the Byzantines also had cannons, the weapons were much smaller than those of the Ottomans, and the recoil tended to damage their own walls.

According to David Nicolle, despite many odds, the idea that Constantinople was inevitably doomed is incorrect, and the overall situation was not as one-sided as a simple glance at a map might suggest.
It has also been claimed that Constantinople was "the best-defended city in Europe" at that time.
The city had about 20 km of walls (land walls: 5.5 km; sea walls along the Golden Horn: 7 km; sea walls along the Sea of Marmara: 7.5 km), one of the strongest sets of fortified walls in existence. The walls had recently been repaired (under John VIII) and were in fairly good shape, giving the defenders sufficient reason to believe that they could hold out until help from the West arrived. In addition, the defenders were relatively well-equipped with a fleet of 26 ships: 5 from Genoa, 5 from Venice, 3 from Venetian Crete, 1 from Ancona, 1 from Aragon, 1 from France, and about 10 from the empire itself.
On 5 April, the Sultan himself arrived with his last troops, and the defenders took up their positions. As Byzantine numbers were insufficient to occupy the walls in their entirety, it had been decided that only the outer walls would be manned. Constantine and his Greek troops guarded the Mesoteichion, the middle section of the land walls, where they were crossed by the river Lycus. This section was considered the weakest spot in the walls and an attack was feared here most. Giustiniani was stationed to the north of the emperor, at the Charisian Gate (Myriandrion); later during the siege, he was shifted to the Mesoteichion to join Constantine, leaving the Myriandrion to the charge of the Bocchiardi brothers. Minotto and his Venetians were stationed in the Blachernae Palace, together with Teodoro Caristo, the Langasco brothers, and Archbishop Leonardo of Chios.
To the left of the emperor, further south, were the commanders Cataneo, who led Genoese troops, and Theophilus Palaeologus, who guarded the Pegae Gate with Greek soldiers. The section of the land walls from the Pegae Gate to the Golden Gate (itself guarded by a Genoese called Manuel) was defended by the Venetian Filippo Contarini, while Demetrius Cantacuzenus had taken position on the southernmost part of the Theodosian wall.
The sea walls were manned more sparsely, with Jacobo Contarini at Stoudion, a makeshift defence force of Greek monks to his left hand, and Prince Orhan at the Harbour of Eleutherios. Pere Julià was stationed at the Great Palace with Genoese and Catalan troops; Cardinal Isidore of Kiev guarded the tip of the peninsula near the boom. Finally, the sea walls at the southern shore of the Golden Horn were defended by Venetian and Genoese sailors under Gabriele Trevisano.
Two tactical reserves were kept behind in the city: one in the Petra district just behind the land walls and one near the Church of the Holy Apostles, under the command of Loukas Notaras and Nicephorus Palaeologus, respectively. The Venetian Alviso Diedo commanded the ships in the harbour.
Although the Byzantines also had cannons, the weapons were much smaller than those of the Ottomans, and the recoil tended to damage their own walls.
According to David Nicolle, despite many odds, the idea that Constantinople was inevitably doomed is incorrect, and the overall situation was not as one-sided as a simple glance at a map might suggest. It has also been claimed that Constantinople was "the best-defended city in Europe" at that time.
Fall of Constantinople