Istanbul (Turkish: İstanbul), historically known as Byzantium and Constantinople is the largest city in Turkey and 5th largest city proper in the world with a population of 12.8 million, also making it the second largest metropolitan area in Europe by population, and the largest metropolitan city proper.
During its long history, Istanbul had previously served as the capital of the Roman Empire (330–c.395), Byzantine Empire (c.395–1204 & 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). Thereafter, the new Republic of Turkey, moved their capital to Ankara during the Turkish War of Independence. Istanbul was chosen as a European Capital of Culture for 2010 and European Capital of Sports for 2012.The historic areas of the city were added to the UNESCO World Heritage List in 1985.
Recent construction of the Marmaray tunnel unearthed a Neolithic settlement underneath Yenikapı on Istanbul's peninsula. Dating back to the 7th millennium BC, before the Bosphorus was even formed, the discovery indicated that the peninsula was settled thousands of years earlier than previously thought. Thracian tribes established two settlements—Lygos and Semistra—on the Sarayburnu, near where Topkapı Palace now stands, between the 13th and 11th centuries BC. On the Asian side, artifacts have been found in Fikirtepe (present-day Kadıköy) that date back to the Chalcolithic period. The same location was the site of a Phoenician trading post at the beginning of the 1st millennium BC as well as the town of Chalcedon, which was established by Greek settlers from Megara in 685 BC.
However, the history of Istanbul generally begins around 660 BC,when the settlers from Megara, under the command of King Byzas, established Byzantion (Latinised as Byzantium) on the European side of the Bosphorus. By the end of the century, an acropolis was established at the former locations of Lygos and Semistra, on the Sarayburnu.
The city experienced a brief period of Persian rule at the turn of the 5th century BC, but the Greeks recaptured it during the Greco-Persian Wars. Byzantium then continued as part of the Athenian League and its successor, the Second Athenian Empire, before ultimately gaining independence in 355 BC. Long protected by the Roman Republic, Byzantium officially became a part of the Roman Empire in AD 73.
Byzantium's decision to side with the usurper Pescennius Niger against Roman Emperor Septimus Severus cost it dearly; by the time it surrendered at the end of 195, two years of siege had left the city devastated. Still, five years later, Severus began to rebuild Byzantium, and the city regained—and, by some accounts, surpassed—its previous prosperity.
When Constantine I defeated Licinius at the Battle of Chrysopolis in September 324, he effectively became the emperor of the whole of the Roman Empire.Just two months later, Constantine laid out the plans for a new, Christian city to replace Byzantium. Intended to replace Nicomedia as the eastern capital of the empire, the city was named Nea Roma (New Rome); however, most simply called it Constantinople ("the city of Constantine"), a name that persisted into the 20th century. Six years later, on 11 May 330, Constantinople was proclaimed the capital of an empire that eventually became known as the Byzantine Empire or Eastern Roman Empire.
The establishment of Constantinople served as one of Constantine's most lasting accomplishments, shifting Roman power eastward and becoming a center of Greek culture and Christianity. Numerous churches were built across the city, including the Hagia Sofia, which remained the world's largest cathedral for a thousand years. The Ecumenical Patriarchate of Constantinople developed in the city, and its leader is still one of the foremost figures in the Greek Orthodox Church. Constantinople's location also ensured its existence would stand the test of time; for many centuries, its walls and seafront protected Europe against invaders from the east as well as from the advance of Islam. During most of the Middle Ages and the latter part of the Byzantine period, Constantinople was the largest and wealthiest city in the western world.
The Fall of Constantinople in 1453 signaled the end of the Byzantine Empire.Constantinople began to decline after the Fourth Crusade, during which it was sacked and pillaged. The city subsequently became the center of the Latin Empire, created by Catholic crusaders to replace the Orthodox Byzantine Empire, which was divided into splinter states.However, the Latin Empire was short-lived, and the Byzantine Empire was restored, weakened, in 1261. Constantinople's churches, defenses, and basic services were in disrepair,and its population had dwindled to forty thousand from nearly half a million during the 9th century.
Various economic and military policies instituted by Andronikos II, such as the reduction of forces, weakened the empire and left it more vulnerable to attack.In the mid-14th century, the Ottoman Turks began a strategy by which they took smaller towns and cities over time, cutting off Constantinople's supply routes and strangling it slowly. Finally, on 29 May 1453, after an eight-week siege (during which the last Roman Emperor, Constantine XI, was killed), Sultan Mehmed II "the Conqueror" captured Constantinople and declared it the new capital of the Ottoman Empire. Hours later, the sultan rode to the Hagia Sofia and summoned an imam to proclaim the Islamic creed, converting the grand cathedral into an imperial mosque.