İstanbul

i.The Two Continents and the Three Seas

İstanbul is the only great city of the world that stands on two continents. The historic peninsula — the triangular promontory enclosed by the Sea of Marmara to the south, the Golden Horn (Haliç) to the north, and the Bosphorus (Boğaz) strait to the east — is European; the older Asian-side districts of Üsküdar, Kadıköy, and Anadolu Hisarı sit across the strait, in Anatolia. The Bosphorus itself, thirty-one kilometres long and at its narrowest only seven hundred metres wide, is the single waterway that connects the Black Sea to the Sea of Marmara, and through the Çanakkale strait to the Aegean and the Mediterranean. Every ship that crosses between the Black Sea world and the Mediterranean world has, for twenty-seven centuries, passed through the city's heart.

It is this geography — a deep natural harbour, a defensible peninsula, control of the only sea passage between two great basins — that explains every layer of the city's history. The Greek geographer Strabo, writing in the 1st century BCE, already understood it: "no city on earth is so well placed for commerce, for naval power, and for the receipt of all the goods of the world."

ii.Byzantion — the Megarian Foundation

The first city on the peninsula is traditionally dated to 657 BCE, when a group of Greek colonists from the small Doric city of Megara on the Saronic Gulf, led — in the legend Britannica preserves — by a captain named Byzas, established a settlement on the high point of the peninsula above the Golden Horn. They named it Byzantion (Latin Byzantium) after their leader. The Megarians, who had earlier founded Chalcedon on the Asian side, were attracted by exactly the same things that would attract every later occupant: the deep, sheltered Golden Horn harbour; the easy defence of a peninsula; and the control over the Black Sea grain trade on which much of the Greek world fed.

Byzantion was, through its long Greek and Hellenistic centuries, a moderately important but not pre-eminent city. It came in and out of Athenian, Spartan, and Persian spheres of influence; it was briefly part of Alexander's empire and then of the Hellenistic kingdoms of his successors. In 196 CE, having taken the wrong side in a Roman civil war, it was razed by the emperor Septimius Severus, who then rebuilt it on a slightly larger plan and briefly renamed it Augusta Antonina in honour of his son. The renamed coinage did not stick; the city was Byzantion until it was something else.

iii.Constantinople — Constantine's New Rome (330 CE)

The transformation came in 324 CE, when the emperor Constantine I defeated his rival Licinius at the battle of Chrysopolis (on the Asian side of the Bosphorus, opposite Byzantion) and decided to refound the city as the new eastern capital of the Roman empire. The new city walls — three times the area of Severus's town — went up over six years; the new city was dedicated on 11 May 330 with games, processions, and the placement of a porphyry column (the Çemberlitaş in modern Turkish) crowned with a statue of Constantine himself. Officially the new foundation was the Nova Roma, the New Rome; in practice it was almost immediately called Konstantinoupolis, the City of Constantine, and that name — Constantinople — would attach to it for the next eleven hundred years.

Constantine moved the senate, the imperial offices, and the resources of the eastern provinces to the new capital. The senate built itself, the great churches and the imperial palace went up around the Hippodrome and Hagia Sophia, and the population — fed by the Egyptian grain that had previously gone to Rome — grew, within a century, to several hundred thousand. By the time the western Roman empire fragmented in the 5th century, Constantinople had become, simply, the capital of what later historians would call the Byzantine empire — the eastern Roman empire continued under Greek-speaking emperors for another thousand years.

iv.Justinian and the Age of Hagia Sophia

The peak of Constantinople's first millennium came under the emperor Justinian I (reigned 527–565). After the Nika riots of 532 had burned most of the central city to the ground, Justinian rebuilt it on an unprecedented scale. The new Hagia Sophia — designed by the mathematicians Anthemius of Tralles and Isidore of Miletus and completed in five years, between 532 and 537 — replaced an earlier basilica on the same site and was, on the day of its consecration, the largest enclosed space the world had yet built. Its great central dome (thirty-one metres in diameter, rising fifty-five metres above the floor) was a structural feat unrivalled in late antiquity. Justinian is reported by the historian Procopius to have said, on entering the finished church: "Solomon, I have surpassed you."

The same period produced the codification of Roman law (the Corpus Juris Civilis, 533–534) and the reconquest of much of the Mediterranean from the Gothic and Vandal kingdoms. Constantinople in the 6th century was, briefly, the capital of a renewed Roman empire that ran from the Caucasus to the Strait of Gibraltar. The reconquest could not be sustained; the plague of 541–549 broke the population; but the buildings of Justinian — the Hagia Sophia above all, but also Saint Irene (Aya İrini), the great underground cisterns (the Yerebatan Sarnıcı survives), and the rebuilt city walls — set the architectural and symbolic vocabulary that the Byzantine empire would carry to its end.

v.From the Crusader Sack to the Palaiologan Recovery

Through the central Byzantine centuries (7th to 11th) Constantinople was, in essence, the only metropolis west of Baghdad. The Arab sieges of the 7th and 8th centuries were repulsed at its walls; the Bulgar pressure of the 9th and 10th was contained; the great trans-Eurasian trade in silk, fur, slaves, and spices ran through its quay-side warehouses. The arrival of the Venetians and the Genoese in the 11th and 12th centuries broke the imperial commercial monopoly and inserted a permanent foreign mercantile colony — the Galata quarter on the northern side of the Golden Horn — that would shape the city's commercial life until the Republic.

The catastrophe came in 1204. The Fourth Crusade, diverted from its declared destination of the Holy Land by the politics of the Venetian doge Enrico Dandolo and the contested Byzantine succession, stormed and sacked Constantinople over three days in April. The city's wealth — the relics of the eastern church, the great bronzes of the Hippodrome (the four horses now over the porch of San Marco in Venice), the libraries — was carried off west; a Latin empire was set up in the city under Baldwin of Flanders. Constantinople would not fully recover. The Byzantine successor state at Nicaea, under the Palaiologos dynasty, retook the city in 1261, but the empire that resumed was a regional principality, shrinking by the decade, holding little more than the city itself and a few coastal districts.

vi.29 May 1453 — the Conquest

The Ottoman conquest was the culmination of a long pressure. The Ottoman emirate, founded by Osman around 1300 in the Bithynian hills opposite the Sea of Marmara, had taken the surrounding country piece by piece through the 14th and early 15th centuries: Bursa (1326), Edirne (1369), Thessaloniki (1430). By the time Sultan Mehmed II — twenty-one years old, in his second reign — moved on Constantinople in the spring of 1453, the city was a small island in an Ottoman sea, with a Greek-speaking population probably below fifty thousand and a Byzantine emperor, Constantine XI Palaiologos, who governed not much more than the walls themselves.

The siege opened on 6 April 1453. Mehmed had assembled an army of perhaps eighty thousand men, a fleet, and — decisively — a train of massive bronze cannon cast for him by the Hungarian gunsmith Orban, the largest of which threw stone shot of more than five hundred kilograms. The cannon could not be reloaded quickly, but they could break the great Theodosian land walls in ways that no earlier siege weapon had. On the night of 22–23 April, in one of the most theatrically remembered actions of the campaign, the Ottoman fleet was hauled overland on greased timbers across the heights of Galata and launched into the Golden Horn, opening the city's northern flank. The land walls fell to the artillery; the final assault, on the night of 28–29 May 1453, broke through the breach near the Romanos Gate (Topkapı in modern Turkish). Constantine XI died fighting at the wall. By midday on Tuesday, 29 May 1453, Mehmed rode through the streets to Hagia Sophia, ordered the building cleared and rededicated as the imperial mosque Ayasofya, and the conquest was complete. The Byzantine empire — eleven hundred and twenty-three years from the dedication of Constantine's New Rome — was at an end.

vii.The Ottoman Capital — 470 Years

Mehmed II rebuilt the captured city as the capital of the Ottoman empire — a city that for the next 470 years would be, by most plausible measures, the largest in Europe. The population, badly depleted by the siege, was rebuilt by an organised programme of resettlement (the sürgün): Greek, Armenian, and Jewish communities were settled in their own quarters; Muslim populations were brought in from the Anatolian provinces; the Sephardic Jewish refugees from Spain were welcomed in 1492 by Bayezid II ("the Catholic Monarchs have impoverished their kingdom and enriched mine," he is reputed to have said). By the mid-16th century the city had perhaps half a million inhabitants, and the polyglot, multi-confessional civic order that the Valilik's own history calls "the most splendid model of living together" was in place.

The 16th century is the architectural age of the city. Under Süleyman the Magnificent (reigned 1520–1566) and his chief architect Mimar Sinan (1490–1588), the skyline took the form it still has: the Süleymaniye complex on the third hill (1557); the Şehzade mosque (1548); the smaller and arguably more perfect Mihrimah Sultan mosques at Edirnekapı and Üsküdar; the Selimiye at Edirne (which Sinan himself called his masterpiece — see our Edirne essay). The 17th century added the Sultan Ahmed mosque (the Blue Mosque, 1616) opposite Hagia Sophia, the Yeni Cami at Eminönü (completed 1665), and the Topkapı Sarayı palace complex as it now stands. The Bosphorus filled with the yalı — the waterfront wooden palaces — of the imperial household and the great Ottoman families.

viii.The Republic, the Capital Move, and the Modern City

Ottoman İstanbul ended with the empire. From 13 November 1918 to 6 October 1923 the city was under Allied occupation. The National Struggle was prosecuted from Ankara on the central plateau; the National Assembly that established the Republic was seated there; and on 13 October 1923, by act of parliament, Ankara — not İstanbul — became the capital of the new Türkiye. The displacement was deliberate: the new Republic was an Anatolian project, looking inland, and the imperial-cosmopolitan city of the Bosphorus had to be put, in symbolic terms, at one remove from the seat of power. İstanbul lost its government, much of its imperial bureaucracy, and over the following decades a great deal of its non-Muslim population.

The 20th century reshaped the city physically as well. The 1950s and 60s brought the first wave of rural-to-urban migration that would, over fifty years, raise the metropolitan population from about a million in 1950 to fifteen million today. The two Bosphorus bridges — the 15 Temmuz Şehitler Köprüsü (1973), formerly the First Bosphorus Bridge, and the Fatih Sultan Mehmet Köprüsü (1988) — and the third Yavuz Sultan Selim Köprüsü (2016), together with the Marmaray rail tunnel (2013) and the Avrasya Tüneli road tunnel (2016), made the two continents into a single working metropolitan area. Modern İstanbul is also Türkiye's financial capital: the Borsa İstanbul stock exchange and most of the country's private banks are headquartered here, and the city accounts for roughly thirty percent of the national economy.

Under TÜİK's 2024 address-based registration count, the province population was 15,701,602 — almost one in five inhabitants of Türkiye. The metropolitan municipality covers 39 districts — twenty-five on the European side, fourteen on the Asian. The largest by population are the modern outer European districts of Esenyurt, Küçükçekmece, and Bağcılar; the most historically dense are Fatih on the old peninsula, Beyoğlu across the Golden Horn, and Üsküdar and Kadıköy on the Asian shore.

ix.UNESCO and the Historic Areas (1985)

In 1985, UNESCO inscribed the Historic Areas of İstanbul on the World Heritage List under four cultural criteria — (i), (ii), (iii) and (iv) — for its unique witness to the Byzantine and Ottoman empires and to the meeting between them. The inscription does not cover the whole city but four named zones on the historic peninsula and immediately across the Golden Horn: the archaeological park at the tip of the peninsula (Hagia Sophia, the Hippodrome, Topkapı, Sultanahmet); the Süleymaniye conservation area on the third hill; the Zeyrek area around the Pantokrator monastery (now Molla Zeyrek Mosque); and the Theodosian land walls from the Marmara to the Golden Horn. Together they preserve, within the modern city, the urban tissue of both the imperial capitals — Byzantine and Ottoman — that the peninsula has carried.

x.What to See, in Order

The walking shape of the historic peninsula is, despite the size of the modern city, small. The classic morning circuit begins at the Sultanahmet Meydanı — the open square that occupies the site of the Byzantine Hippodrome — with the still-standing Egyptian Obelisk of Theodosius, the Serpent Column from Delphi, and the Walled Obelisk at its centre. Around it stand the two great religious monuments of the city's two civilisations: Hagia Sophia (532–537, re-mosqued in 2020) and the Sultan Ahmed Camii (the Blue Mosque, 1616). North of the square, the Topkapı Sarayı palace complex (1465 onward) holds the Treasury, the Holy Relics, and the eastern view across the Bosphorus. South of it, the Yerebatan Sarnıcı (the Basilica Cistern, 6th century) holds its column-forest of Justinianic Constantinople under twenty centimetres of water.

An afternoon walk leads west, through the Kapalıçarşı (the Grand Bazaar, 1461 onward) and the Mısır Çarşısı (the Spice Bazaar, 1664) at Eminönü, up the hill of the third bridge to the Süleymaniye Camii (1557) — Sinan's largest Constantinople work — and then back along the Golden Horn quayside to the Atatürk Bridge. A separate day takes the visitor up the Bosphorus by boat, past the wooden yalı of the European and Asian shores, the Rumeli Hisarı (1452, built by Mehmed II to close the strait for the conquest), and the great 19th-century palaces — Dolmabahçe and Çırağan — on the western quay. The Asian side is its own day: the steamer to Kadıköy, the lunch of fish and rakı at the Sunday market on Moda, and the long walk up the shore to the Beylerbeyi palace and the green hill of Çamlıca.

The only great city of the world that stands on two continents — Byzantion, Constantinople, İstanbul — and which has been, in turn, the capital of three empires and the metropolis of a Republic.

For the Ottoman capital that preceded İstanbul, see our Bursa essay; for the Ottoman "second capital" in Thrace, see Edirne. For the inland republican capital that replaced İstanbul in 1923, see Ankara. For Türkiye's geography in the wider sense, visit our sister site CountryOfTurkey.com.