Mehmed built a fleet (partially manned by Spanish sailors from Gallipoli) to besiege the city from the sea.
Contemporary estimates of the strength of the Ottoman fleet span from 110 ships to 430. (
Tedaldi: 110; Barbaro: 145; Ubertino Pusculo: 160, Isidore of Kiev and Leonardo di Chio: 200–250; (Sphrantzes): 430) A more realistic modern estimate predicts a fleet strength of 110 ships comprising 70 large galleys, 5 ordinary galleys, 10 smaller galleys, 25 large rowing boats, and 75 horse-transports.

Before the siege of Constantinople, it was known that the Ottomans had the ability to cast medium-sized cannons, but the range of some pieces they were able to field far surpassed the defenders' expectations.
The Ottomans deployed a number of cannons, anywhere from 50 cannons to 200.
They were built at foundries that employed Turkish cannon founders and technicians, most notably Saruca, in addition to at least one foreign cannon founder, Orban (also called Urban).
Most of the cannons at the siege were built by Turkish engineers, including a large bombard by Saruca, while one cannon was built by Orban, who also contributed a large bombard.

Orban, a Hungarian (though some suggest he was German), was a somewhat mysterious figure.
His 27 feet (8.2 m) long cannon was named "Basilica" and was able to hurl a 600 lb (270 kg) stone ball over a mile (1.6 km).
Orban initially tried to sell his services to the Byzantines, but they were unable to secure the funds needed to hire him.
Orban then left Constantinople and approached Mehmed II, claiming that his weapon could blast "the walls of Babylon itself".
Given abundant funds and materials, the Hungarian engineer built the gun within three months at Edirne.
However, this was the only cannon that Orban built for the Ottoman forces at Constantinople, and it had several drawbacks: it took three hours to reload; cannonballs were in very short supply; and the cannon is said to have collapsed under its own recoil after six weeks.
The account of the cannon's collapse is disputed, given that it was only reported in the letter of Archbishop Leonardo di Chio and in the later, and often unreliable, Russian chronicle of Nestor Iskander.

Having previously established a large foundry about 150 miles (240 km) away, Mehmed now had to undertake the painstaking process of transporting his massive artillery pieces.
In preparation for the final assault, Mehmed had an artillery train of 70 large pieces dragged from his headquarters at Edirne, in addition to the bombards cast on the spot.
This train included Orban's enormous cannon, which was said to have been dragged from Edrine by a crew of 60 oxen and over 400 men.
There was another large bombard, independently built by Turkish engineer Saruca, that was also used in the battle.

Mehmed planned to attack the Theodosian Walls, the intricate series of walls and ditches protecting Constantinople from an attack from the West and the only part of the city not surrounded by water.
His army encamped outside the city on 2 April 1453, the Monday after Easter.

The bulk of the Ottoman army was encamped south of the Golden Horn.
The regular European troops, stretched out along the entire length of the walls, were commanded by Karadja Pasha.
The regular troops from Anatolia under Ishak Pasha were stationed south of the Lycus down to the Sea of Marmara.
Mehmed himself erected his red-and-gold tent near the Mesoteichion, where the guns and the elite Janissary regiments were positioned.
The Bashi-bazouks were spread out behind the front lines.
Other troops under Zagan Pasha were employed north of the Golden Horn.
Communication was maintained by a road that had been destroyed over the marshy head of the Horn.
Mehmed built a fleet (partially manned by Spanish sailors from Gallipoli) to besiege the city from the sea. Contemporary estimates of the strength of the Ottoman fleet span from 110 ships to 430. (Tedaldi: 110; Barbaro: 145; Ubertino Pusculo: 160, Isidore of Kiev and Leonardo di Chio: 200–250; (Sphrantzes): 430) A more realistic modern estimate predicts a fleet strength of 110 ships comprising 70 large galleys, 5 ordinary galleys, 10 smaller galleys, 25 large rowing boats, and 75 horse-transports.
Before the siege of Constantinople, it was known that the Ottomans had the ability to cast medium-sized cannons, but the range of some pieces they were able to field far surpassed the defenders' expectations. The Ottomans deployed a number of cannons, anywhere from 50 cannons to 200. They were built at foundries that employed Turkish cannon founders and technicians, most notably Saruca, in addition to at least one foreign cannon founder, Orban (also called Urban). Most of the cannons at the siege were built by Turkish engineers, including a large bombard by Saruca, while one cannon was built by Orban, who also contributed a large bombard.
Orban, a Hungarian (though some suggest he was German), was a somewhat mysterious figure. His 27 feet (8.2 m) long cannon was named "Basilica" and was able to hurl a 600 lb (270 kg) stone ball over a mile (1.6 km). Orban initially tried to sell his services to the Byzantines, but they were unable to secure the funds needed to hire him. Orban then left Constantinople and approached Mehmed II, claiming that his weapon could blast "the walls of Babylon itself". Given abundant funds and materials, the Hungarian engineer built the gun within three months at Edirne. However, this was the only cannon that Orban built for the Ottoman forces at Constantinople, and it had several drawbacks: it took three hours to reload; cannonballs were in very short supply; and the cannon is said to have collapsed under its own recoil after six weeks. The account of the cannon's collapse is disputed, given that it was only reported in the letter of Archbishop Leonardo di Chio and in the later, and often unreliable, Russian chronicle of Nestor Iskander.
Having previously established a large foundry about 150 miles (240 km) away, Mehmed now had to undertake the painstaking process of transporting his massive artillery pieces. In preparation for the final assault, Mehmed had an artillery train of 70 large pieces dragged from his headquarters at Edirne, in addition to the bombards cast on the spot. This train included Orban's enormous cannon, which was said to have been dragged from Edrine by a crew of 60 oxen and over 400 men. There was another large bombard, independently built by Turkish engineer Saruca, that was also used in the battle.
Mehmed planned to attack the Theodosian Walls, the intricate series of walls and ditches protecting Constantinople from an attack from the West and the only part of the city not surrounded by water. His army encamped outside the city on 2 April 1453, the Monday after Easter.
The bulk of the Ottoman army was encamped south of the Golden Horn. The regular European troops, stretched out along the entire length of the walls, were commanded by Karadja Pasha. The regular troops from Anatolia under Ishak Pasha were stationed south of the Lycus down to the Sea of Marmara. Mehmed himself erected his red-and-gold tent near the Mesoteichion, where the guns and the elite Janissary regiments were positioned. The Bashi-bazouks were spread out behind the front lines. Other troops under Zagan Pasha were employed north of the Golden Horn. Communication was maintained by a road that had been destroyed over the marshy head of the Horn.
Fall of Constantinople