Istanbul through the ages

Digging for the Yenikapı metro station and the Marmaray tunnel turned up, in 2008, the earliest known settlement on the historic peninsula, dating from 6700 BC. A settlement stood near the point of the peninsula in the early 1st millennium BC, linked by modern authors to Lygos, the name Pliny the Elder gives for the site before Byzantium.

The city proper begins with Greek settlers from the Attic town of Megara, who founded Byzantion on the European side of the Bosphorus in the seventh century BC; the accounts differ over the year, 667 BC in one telling and around 657 to 660 BC in others. The colonists built an acropolis beside the Golden Horn, on the site of the earlier Thracian settlements, and it was the strait that made the place: shipping had to pass it. Byzantion was briefly under Persian rule at the turn of the 5th century BC, belonged afterwards to the Athenian League and its successor, won independence in 355 BC and became formally part of the Roman Empire in 73 AD. Backing the usurper Pescennius Niger against Septimius Severus cost it dearly: two years of siege left it devastated by its surrender at the end of 195 AD, and Severus began rebuilding five years later.

Constantine the Great became emperor of the whole Roman Empire after defeating Licinius at Chrysopolis on the Bosphorus on 18 September 324, and two months later laid out plans for a new Christian city to replace Byzantium. He called it Nova Roma; almost everyone called it Constantinople. It was proclaimed capital of the Roman Empire on 11 May 330, and on the death of Theodosius I in 395 the empire was divided permanently between his sons, leaving Constantinople the capital of the eastern half.

The city lived off its position at the crossing between Europe and Asia, and off the imperial administration it housed. Nicene Christianity became the official religion of the empire in 381, and the city became the centre of the Greek world and the seat of the Patriarch of Constantinople; Hagia Sophia, built under Justinian I, remained the world's largest cathedral for a thousand years. Under Justinian, who reigned from 527 to 565, the population approached half a million. For most of the Byzantine period this was the largest city in Europe, and the walls and seafront shielded it for centuries against attack from the east.

Decline set in after the reign of Basil II ended in 1025. In 1204 the Fourth Crusade was diverted from Jerusalem: western armies took Constantinople and stripped it of its treasures, Hagia Sophia was converted to a Catholic church, and Baldwin of Flanders was made Latin Emperor while the crusading princes and the Republic of Venice divided the empire between them. The Byzantines under Michael VIII Palaiologos retook the city in 1261, but its churches, defences and basic services were in disrepair and its population had fallen to about a hundred thousand from half a million in the 8th century.

What followed was not recovery. The city became a scattering of villages inside its walls — Ibn Battuta noted fields sown within them — and by 1453 held less than a tenth of its former population. From the mid-14th century the Ottomans took the smaller towns around it one by one, cutting the supply routes and strangling it slowly.

Mehmed II began the siege on 6 April 1453 with cannon built for the purpose, and entered the city on 29 May; the length of the siege is given as 53 days in one account and 55 in another. In accordance with Islamic law he had offered the emperor Constantine XI three chances to surrender, guaranteeing the residents their riches, beliefs and honour, and been refused. The Theodosian walls were breached in two places, Constantine XI was killed in the fighting, and Mehmed rode to Hagia Sophia and had an imam proclaim the Muslim creed there, converting the cathedral into an imperial mosque because the city had not surrendered peacefully. He ordered three days of plunder.

Most of what remained of the Byzantine population, some 30,000 people, was deported. Repopulating the city then became the sultan's main concern. He issued orders across the empire that Muslims, Christians and Jews should resettle it and that five thousand households be deported there by September, and in 1459 allowed Greeks who had left as slaves or refugees to return. The chronicle of Ashikpashazade records that when an offer of freehold houses and gardens failed to fill the city, "the Sultan commanded that from every land families, rich and poor alike, should be brought in by force". The census of 1477 counted 9,486 households of Muslims, 3,743 of Greeks, 1,647 of Jews and 267 of Christians from the Crimea. The Italians of Galata, who had surrendered before the city fell, kept a measure of self-government and supplied the Ottoman court with interpreters and diplomats for generations, and Mehmed re-established the city as the seat of the Orthodox patriarchate. The Grand Bazaar was built in 1455, Topkapı Palace in 1459 and the Fatih mosque and college in 1463, on the burial ground of the Byzantine emperors.

After the conquest of Egypt in 1517 the Ottoman dynasty claimed the caliphate, and the city remained its seat for four centuries. Under Suleiman the Magnificent, who reigned from 1520 to 1566, the chief architect Mimar Sinan built many of its mosques while ceramics and calligraphy flourished. Its communities lived in self-contained quarters, but plague made no such distinctions, killing rich and poor alike through the 16th century.

The population grew from about 80,000 at Mehmed II's death to some 300,000 by the 18th century and 400,000 in 1800, though a higher count of 570,000 by the end of the 18th century is also given. Rebellion at the start of the 19th century brought Mahmud II to power and led to the Tanzimat reforms; bridges were thrown across the Golden Horn, the city was joined to the European railway network in the 1880s, and a water network, electricity, telephones and trams followed, later than in other European cities. None of it forestalled the decline of the empire.

The Young Turk Revolution reopened the Ottoman Parliament on 23 July 1908 after thirty years, Abdul Hamid II was deposed in 1909, and the Balkan wars were followed by the coup of 1913 that brought the regime of the Three Pashas. The empire entered the First World War on the side of the Central Powers. The deportation of Armenian intellectuals from the city on 24 April 1915 was among the events that marked the start of the Armenian genocide. Between 1914 and 1927 the city's Christian population fell from 450,000 to 240,000 as a result of Ottoman and Turkish policies of Turkification and ethnic cleansing. An Allied operation to capture the city failed when the Ottoman army repulsed the British and ANZAC landing force in the Gallipoli campaign.

The Armistice of Mudros was signed on 30 October 1918 and a French brigade entered the city on 12 November, followed the next day by British, Italian, Greek and French troops. The Allies dissolved the Ottoman Parliament on 11 April 1920, and many of its members joined the national movement whose Grand National Assembly was established at Ankara that month; the Istanbul government's signature on the Treaty of Sèvres that August was rejected there. The Assembly abolished the sultanate on 1 November 1922 and the last sultan, Mehmed VI, left aboard a British warship on 17 November. The Treaty of Lausanne was signed on 24 July 1923; the last Allied forces left on 4 October and Turkish troops entered the city two days later.

The Republic was declared on 29 October 1923 with Ankara as its capital, and the city that had been the capital of four empires was overlooked in favour of the new capital, and its population fell from an estimated 1,125,000 in 1914 to about 500,000 in 1924. The name Constantinople, in use for sixteen centuries, was officially replaced by İstanbul under the Postal Services Law of 28 March 1930. From 1936 large-scale planning under Henri Prost and his successors cut new squares, boulevards and avenues through the city, often demolishing historic buildings.

The wealth tax of 1942 was levied at much higher rates on non-Muslims and forced the transfer or liquidation of many businesses owned by religious minorities. During the Istanbul pogrom of September 1955 Greek businesses were destroyed and Greeks were killed, wounded and sexually assaulted; Jews, Armenians and Georgians were also targeted, and most of the remaining Greeks left. Further mass expulsions followed in 1964–65, when Greek citizens who had been exempted from the population exchange under the Treaty of Lausanne were ordered out of the country, spouses holding Turkish citizenship included, after Turkey and Greece came close to war over Cyprus. The city's Greek population fell from 110,000 in 1919 to 2,500 by the end of the 20th century. The Theological School of Halki closed in 1971 rather than accept attachment to Istanbul University under a law nationalising private higher education, and minority emigration to Europe and North America continued through the political turmoil of 1960 to 1980.

From the 1970s the population climbed steeply as people came from Anatolia to work in the new factories on the outskirts; housing demand swallowed outlying villages and forests, and the Bosphorus Bridge, opened in 1973, drew still more migration. In March 1995 twenty-three people were killed and hundreds injured in the Gazi Massacre, which began with an armed attack on coffee shops in the neighbourhood in which an Alevi religious leader was killed and continued when police fired on the protests that followed. Taksim Square was the centre of the Gezi Park protests in 2013 over press freedom, assembly and the government's encroachment on secularism, and soldiers taking part in the attempted coup of July 2016 surrendered on the Bosphorus Bridge. Bomb attacks killed ten German tourists at Sultanahmet in January 2016, thirty-eight outside the Beşiktaş stadium that December, thirty-nine at a nightclub on 1 January 2017 and six on İstiklal Avenue in November 2022.

Istanbul is the largest city in Turkey and home to 18% of its people, with a population of over 15 million, about two-thirds of them on the European side of the Bosphorus. Its Kurdish population, estimated at between two and four million, is the largest minority among Turkish citizens in the city, and as of August 2023 it held more than 530,000 refugees of the Syrian civil war, the highest number of any Turkish city.