Istanbul

Istanbul is the largest city and principal seaport of Turkey, and it served as the capital of two empires in succession. It has been known by several names: Byzantium, Constantinople, New Rome and Augusta Antonina. The city was founded about 657 BCE as the Greek colony of Byzantium. The city has been associated with major events in political history, religious history and art history for more than 2,000 years.

The name Byzantium may derive from Byzas, the leader of the Greeks from Megara who, according to legend, captured the peninsula from pastoral Thracian tribes. The Strait of Bosporus linked the Black Sea with the Mediterranean Sea. Modern historians would later apply the name Byzantium to the Christian, ultimately Greek-speaking state ruled from Constantinople, even though its citizens described themselves as Rhomaioi, Romans.

In 196 CE, having razed the town for opposing him in a civil war, the Roman emperor Septimius Severus rebuilt it and named it Augusta Antonina in honour of his son. Constantine I came into power in the western half of the empire in 312 CE and reunited it by defeating Licinius at the Battle of Chrysopolis in 324 CE.

By the 13th century the Greek phrase eis ten polin, used for trips into the city, had become an appellation for it, Istinpolin, which through speech permutations over centuries became Istanbul.

Istanbul occupies a position at the junction of Europe, Africa and Asia, a circumstance that made it not only a political and military capital but one of the great trade centres of the world. The historic city sits on a peninsula, and the Bosphorus strait divides the city between its European and Asian sides.

The city's walls ran some 19 km in total, a length that the defending army of fewer than 5,000 men, as numbered by the eyewitness historian Georges Sphrantzes, was too few to cover. Before the final siege, Mehmed II built, extended and occupied fortresses along the Bosphorus, notably Rumeli Hisar and Anadolu in 1452 CE. The inscribed World Heritage property is a serial site, dossier 356bis, covering 765.5 hectares.

The site's legendary foundation is credited to Byzas, with the alternative legendary date of 667 BCE sometimes given alongside the traditional date of about 657 BCE. The settlement was destroyed by Darius in 513 BCE and incorporated into the Achaemenid Empire. After the Battle of Plataea in 478 BCE, Pausanias became governor of the city. It subsequently played a role in the Delian League before later aligning itself with Sparta.

Around 196 CE Septimius Severus razed the city and then rebuilt it. The reconstruction gave the city the Baths of Zeuxippus, the Hippodrome and a protective wall.

On 11 May 324 CE Emperor Constantine the Great selected the city to be the new capital of the reunited Roman Empire and called it New Rome. The imperial capital was thus transferred from Rome, and the city served as the seat of the Byzantine Empire for 1,100 years, its citizens calling themselves Rhomaioi. The empire stood as a bulwark against Arab expansion into Europe, with Constantinople twice withstanding determined Arab sieges, from 674 to 678 and again in 717 to 718 CE. The new capital was consecrated on 11 May 330 CE.

In 1204 armies of the Fourth Crusade conquered the Byzantine imperial capital and founded the Latin Empire of Constantinople. The city was retaken by the Palaeologan dynasty in 1261 although it never regained its previous status.

The site's first church, the Megale Ekklesia, was commissioned by Emperor Constantine I in 325 and razed during a public disturbance in 404; a second church, dedicated in 415 by Theodosius II, burned down during the Nika revolt of 532 CE. Justinian I then commissioned the present building, which was completed on 27 December 537 under his rule and designed by the architects Anthemios of Tralles and Isidoros of Miletos. Conceived as the major basilica of the Byzantine Empire, it held the record for the largest dome in the world until the Duomo was built in Florence in the 15th century. Its dome, more than 101 feet (31 m) in diameter and rising to a height of 160 feet (48.5 m), defines the structure's scale. The first dome collapsed in 558 and was rebuilt in 562 to a greater height.

The Fall of Constantinople on 29 May 1453 was the conquest of the city by Sultan Mehmed II of the Ottoman Empire. The Ottomans breached the city's ancient land wall after besieging it for 55 days. Most historians consider the conquest the event that terminated the Byzantine Empire. The Ottoman Empire later reached its height under Suleiman the Magnificent, who reigned from 1520 to 1566 and expanded it to cover the Balkans and Hungary and to reach the gates of Vienna. The Ottoman Empire officially ended in 1922 when the sultanate was abolished and Turkey was declared a republic.

The Ottoman architectural imprint on the city includes the Topkapi Palace, whose name means Cannon Gate and which served as the imperial residence and headquarters between the 15th and 16th centuries. Among the monuments of the successive imperial periods are the 16th century Sehzade Mosque complex, the Sokollu Mehmet Pasha Mosque, and the 17th century Blue Mosque. The same areas also display the hippodrome of Constantine and the aqueduct of Valens.

The Sultan Ahmed Mosque, known as the Blue Mosque, was completed in 1616 for Sultan Ahmed I and was the work of one of Sinan's disciples.

The Historic Areas of Istanbul were inscribed on the World Heritage List in 1985 under criteria (i)(ii)(iii)(iv), with a minor boundary modification inscribed in the year 2017 by the World Heritage Committee. The inscribed property consists of four areas: the Archaeological Park at the tip of the peninsula, the Suleymaniye quarter, the Zeyrek settlement area and the zone along both sides of the Theodosian land walls. A Site Management Directorate for Cultural and Natural Sites of Istanbul was established within the Istanbul Metropolitan Municipality in 2006 to coordinate management planning for the city's World Heritage sites.

The landward defences of the city were reshaped under Theodosius II, who expanded the walls in 413 CE; the new walls stood forty feet high and sixteen feet thick. The final line of defence was almost 5 metres thick and 12 metres high, and it presented 96 projecting towers to any attacker. Despite the many attacks, prolonged sieges and internal rebellions the city endured, these defences were regarded as the most formidable in both the ancient and medieval worlds. The land walls eventually ran about 4.5 miles (7 km) between an inner and an outer wall protected by a moat. Attackers first faced a ditch 20 metres wide and 7 metres deep, which could be flooded with water fed from pipes when required.

Istanbul's population stood at 10,757,327 in the 2007 count, and by 2019 the urban agglomeration was estimated at 15,113,808 residents.

Three of the world's longest suspension bridges span the Bosporus: the Bosporus I bridge opened in 1973 and was followed by the Fatih Sultan Mehmed bridge in 1988 and the Yavuz Sultan Selim bridge in 2016 across the same strait.

Two tunnels under the Bosporus, one for passenger rail and one for automobile traffic, were opened in 2013 and 2016 respectively.

The urban fabric of the property is reported as threatened by lack of maintenance and pressure for change, while its masterpieces are under threat from population pressure, industrial pollution and uncontrolled urbanization.

• 1453 CE
  Ottoman conquest and conversion of Hagia Sophia
  After Mehmet II's conquest of the city in 1453 CE Hagia Sophia was converted to a mosque.^{12Hagia Sophia, 532-37 · The Metropolitan Museum of Art (Heilbrunn Timeline of Art History) ↗}