Fifty-three days in the spring of 1453 ended the Byzantine Empire and made Istanbul the Ottoman capital. What happened, why, and what can still be seen.
Last reviewed on 27 September 2026.
On 29 May 1453 the Ottoman army of Sultan Mehmed II stormed Constantinople after a siege of some seven weeks. The last Byzantine emperor, Constantine XI Palaiologos, died in the fighting, and a state that traced its continuity back to the Roman Empire came to an end. For the Ottomans it was the conquest (fetih) that made them an imperial power with a capital to match; Mehmed has been known ever since as Fatih, "the Conqueror". This page sets out the background, the course of the siege, the aftermath, and the parts of the traditional story that historians treat with caution.
By the 15th century the Byzantine Empire was a shadow. The Fourth Crusade had sacked Constantinople in 1204, and although the Byzantines recovered the city in 1261, they never regained their former strength. Through the 14th century the Ottomans expanded from their base in northwestern Anatolia into the Balkans, taking Bursa (1326) and Edirne (by about 1369), which became their capital. By 1400 the empire amounted to little more than Constantinople, a few Aegean islands and the Despotate of the Morea in the Peloponnese, and emperors were at times Ottoman vassals.
The city had already been besieged. Bayezid I blockaded it through the 1390s and built the fortress of Anadolu Hisarı on the Asian shore of the Bosphorus; his defeat by Timur at Ankara in 1402 gave Byzantium half a century of reprieve. Murad II besieged the city in 1422 without success. Western help was the Byzantines' only hope, but the crusade of Varna failed in 1444, and the price the papacy demanded — union of the Orthodox and Catholic churches — was deeply unpopular in the city.
Mehmed II, born in 1432, became sultan for the second time in February 1451 at the age of eighteen. Western observers underestimated him. Within a year he had decided on the conquest, and he prepared methodically.
In the spring and summer of 1452 he built Rumeli Hisarı on the European shore at the narrowest point of the Bosphorus, directly opposite his great-grandfather's fortress. Contemporary accounts say the work took about four and a half months, with the sultan's leading commanders each responsible for a tower. With cannon on both shores the Ottomans could close the strait to ships bringing grain and reinforcements from the Black Sea; the fortress was nicknamed Boğazkesen, which means both "strait-cutter" and "throat-cutter". In November 1452 a Venetian ship that refused to stop was sunk and its crew executed. Rumeli Hisarı stands intact today in the Sarıyer district of Istanbul and is open as a museum; check current hours, as it has had long restoration closures.
Constantine XI, emperor since 1449, appealed to Venice, Genoa, the papacy and the Western kings with little result. On 12 December 1452 the union of the churches was formally proclaimed in Hagia Sophia, to the anger of much of the clergy and population. The historian Doukas attributes to the megas doux Loukas Notaras the remark that he would rather see the Turkish turban in the city than the Latin mitre; whether or not he said it, the phrase captures a real division. The most important reinforcement was the Genoese soldier Giovanni Giustiniani Longo, who arrived in January 1453 with about 700 men and was given command of the land walls.
Constantinople was a triangle protected by water on two sides — the Sea of Marmara to the south and the Golden Horn to the north — and by the Theodosian land walls on the west. Built under Theodosius II in the early 5th century and strengthened after an earthquake in 447, they ran about six kilometres from the Marmara to the Golden Horn in three lines: a broad moat, an outer wall with towers, and a massive inner wall with larger towers behind it. For a thousand years they had turned back every attacker who came by land. A great iron chain, floated on wooden booms, could be stretched across the mouth of the Golden Horn to keep enemy ships out of the harbour.
Mehmed's answer was gunpowder artillery on a scale not seen before. A founder called Orban (or Urban), usually described as Hungarian, had first offered his services to Constantine, who could not pay him; he then went to the sultan and cast for him, at Edirne, a giant bronze bombard. Contemporary descriptions speak of a barrel over eight metres long firing stone balls of several hundred kilograms, needing dozens of oxen and hundreds of men to move it to the city. Such figures come from chroniclers and should be treated as approximate. The great gun could fire only a few times a day and is said to have cracked during the siege, but together with many smaller guns it battered the walls continuously for weeks, and the defenders spent every night repairing breaches with timber, earth and rubble. Orban's gun does not survive; the Dardanelles Gun, a similar Ottoman bombard cast in 1464, is in the Royal Armouries collection in Britain.
| Forces (estimates) | Defenders | Ottoman army |
|---|---|---|
| Contemporary accounts | Sphrantzes, the emperor's secretary, counted fewer than 5,000 Greeks able to fight plus about 2,000 foreigners | Figures of 160,000 and more appear in Western accounts, likely exaggerated |
| Modern estimates | Roughly 7,000–8,000 | Commonly placed between about 50,000 and 80,000 fighting men, plus many auxiliaries |
The Ottoman army arrived before the walls in early April, and the bombardment began around 6 April. Mehmed concentrated his main effort on the middle section of the land walls around the valley of the Lycus stream, between the gates now called Topkapı and Edirnekapı, and on the Blachernae area at the northern end.
20 April. Three Genoese ships hired by the pope and a Byzantine grain ship fought their way through the Ottoman fleet and into the Golden Horn in full view of both armies. Accounts describe Mehmed riding his horse into the shallows in fury. The Ottoman admiral, Baltaoğlu Süleyman Bey, was dismissed. The episode showed that the city could not be closed off by sea while the chain held the harbour.
22 April: the ships overland. Mehmed's response was one of the most famous episodes of the siege. Ottoman engineers built a track of greased timbers over the hill behind Galata, and some seventy ships (numbers vary between sources) were hauled by oxen and men from the Bosphorus shore down into the Golden Horn near Kasımpaşa, bypassing the chain; the exact route is debated. The defenders woke to find enemy ships inside their harbour. A Venetian attempt to burn them failed. The move did not break the city, but it forced the defenders to spread thin men along the sea walls of the Golden Horn.
May. The Ottomans dug mines under the walls; the defenders countered them with their own tunnels, directed according to some accounts by an engineer called Johannes Grant. A great siege tower was burned. Morale in the city was sapped by hunger and by omens reported in the chronicles: a lunar eclipse on 22 May and a thick fog and strange light over Hagia Sophia. In the Ottoman camp, too, there were voices, notably the old vizier Çandarlı Halil Pasha, urging Mehmed to make terms, while younger commanders such as Zağanos Pasha pressed for a final assault.
After a day of rest and prayer, the assault began in the early hours of Tuesday 29 May. Mehmed attacked in waves: first irregulars, then Anatolian troops, and finally the Janissaries, his elite infantry. The defenders held for several hours at the main breach. The turning point came when Giustiniani was badly wounded and carried from the walls; his men, seeing him go, began to withdraw, and the Janissaries broke through. Doukas adds that Ottoman soldiers found a small postern gate, the Kerkoporta near Blachernae, left open and raised a flag on the tower behind the defenders. Many historians regard the Kerkoporta story as a later explanation for a collapse that the breach alone would explain.
Constantine XI was last seen fighting near the breach, having thrown off his imperial insignia according to some accounts. His body was never identified with certainty, and in Greek folklore he became the "Marble Emperor" who would one day return. Giustiniani escaped by ship and died of his wounds on Chios. By custom the soldiers were allowed to sack a city taken by storm, and the looting, killing and enslavement that followed are described with horror by Greek and Italian witnesses; many inhabitants were taken captive. Mehmed entered the city the same day, went to Hagia Sophia and ordered it converted into a mosque, where the first Friday prayers were held on 1 June.
Mehmed set out to make the half-empty city his capital and the centre of a world empire. He called himself Kayser-i Rum, Caesar of Rome, and invited scholars and artists to his court, among them the Venetian painter Gentile Bellini, whose portrait of the sultan (attributed to him) is in the National Gallery in London. Galata, the Genoese colony across the Golden Horn, surrendered on terms and kept its churches and trading privileges.
Ottoman documents continued to call the city Kostantiniyye alongside names such as Istanbul and Dersaadet until the end of the empire; "Istanbul", which derives from a Greek phrase meaning "into the city", became the only official name in the early years of the Republic of Turkey.
The siege is unusually well documented, though every source has a viewpoint. On the Byzantine side there are George Sphrantzes, the emperor's friend and secretary (his short chronicle is authentic; the longer version is a 16th-century elaboration), Doukas and Laonikos Chalkokondyles. Kritoboulos of Imbros, a Greek, wrote an admiring history dedicated to Mehmed. Italian eyewitnesses include the Venetian ship's doctor Nicolò Barbaro, who kept a day-by-day diary, and Archbishop Leonard of Chios. Ottoman accounts, such as those of Tursun Bey, who served in the campaign, and Aşıkpaşazade, present the conquest as the fulfilment of a religious promise, citing a hadith attributed to the Prophet praising the commander who would take Constantinople.
Long stretches survive between Yedikule on the Marmara and Ayvansaray on the Golden Horn. Walk the section around Topkapı and Edirnekapı for the main battle zone; some parts are heavily restored.
At Topkapı (the land-wall gate, not the palace), a 360-degree painted panorama of the final assault. Popular with Turkish school groups.
Mehmed's 1452 fortress on the Bosphorus at Sarıyer, with views across to Anadolu Hisarı. Check whether it is open before going.
Hagia Sophia, where Mehmed prayed after the conquest, and the Fatih Mosque with his tomb.
Links said to come from the Golden Horn chain are displayed in the Istanbul Military Museum at Harbiye. In Türkiye, 29 May is marked each year with commemorations of the conquest, particularly in Istanbul.
Constantinople fell to the Ottoman army of Sultan Mehmed II on Tuesday 29 May 1453, after a siege that began in early April. The last Byzantine emperor, Constantine XI Palaiologos, died in the final assault.
A chain across the mouth of the Golden Horn kept the Ottoman fleet out, so on 22 April 1453 Mehmed had some seventy ships hauled overland on greased timbers over the hill behind Galata, from the Bosphorus shore down into the Golden Horn. This forced the defenders to man the sea walls there as well as the land walls.
Orban's giant bronze bombard, cast for Mehmed at Edirne, was the largest gun of the siege, but it could fire only a few times a day. The steady bombardment by it and many smaller guns, week after week, is what wore down the Theodosian walls, which had resisted every earlier attack by land.
Constantine XI was last seen fighting near the main breach in the land walls on 29 May 1453. His body was never identified with certainty, which gave rise to the Greek legend of the Marble Emperor who would one day return to reclaim the city.
No. The name Istanbul was already in everyday use, but Ottoman official documents continued to use Kostantiniyye alongside other names until the end of the empire. Istanbul became the sole official name in the Republican era.
Yes. Long stretches of the Theodosian land walls survive across Istanbul from Yedikule on the Sea of Marmara to Ayvansaray on the Golden Horn. The area between Topkapı and Edirnekapı, where the decisive fighting took place, is the most rewarding to walk, and the Panorama 1453 History Museum is nearby.