Founded under the name of Byzantion () on the Sarayburnu promontory around 660 BC, the city developed to become one of the most significant in history. After its reestablishment as Constantinople in 330 AD, it served as an imperial capital for almost 16 centuries, during the Roman and Byzantine (3301204 and 12611453), the Latin (12041261), and the Ottoman (14531922) empires. It was instrumental in the advancement of Christianity during Roman and Byzantine times, before the Ottomans conquered the city in 1453 and transformed it into an Islamic stronghold and the seat of the Ottoman Caliphate.
Istanbul's strategic position on the historic Silk Road, rail networks to Europe and the Middle East, and the only sea route between the Black Sea and the Mediterranean have produced a cosmopolitan populace, although less so since the establishment of the Turkish Republic in 1923. Overlooked for the new capital Ankara during the interwar period, the city has since regained much of its prominence. The population of the city has increased tenfold since the 1950s, as migrants from across Anatolia have moved in and city limits have expanded to accommodate them. Arts, music, film, and cultural festivals were established at the end of the 20th century and continue to be hosted by the city today. Infrastructure improvements have produced a complex transportation network.
Approximately 12.56 million foreign visitors arrived in Istanbul in 2015, five years after it was named a European Capital of Culture, making the city the world's fifth most popular tourist destination. The city's biggest attraction is its historic center, partially listed as a UNESCO World Heritage Site, and its cultural and entertainment hub can be found across the city's natural harbor, the Golden Horn, in the Beyolu district. Considered a global city, Istanbul has one of the fastest-growing metropolitan economies in the world. It hosts the headquarters of many Turkish companies and media outlets and accounts for more than a quarter of the country's gross domestic product. Hoping to capitalize on its revitalization and rapid expansion, Istanbul has bid for the Summer Olympics five times in twenty years.
The first known name of the city is Byzantium (Greek: , Byzntion), the name given to it at its foundation by Megarean colonists around 660 BCE. The name is thought to be derived from a personal name, Byzas. Ancient Greek tradition refers to a legendary king of that name as the leader of the Greek colonists. Modern scholars have also hypothesized that the name of Byzas was of local Thracian or Illyrian origin and hence predated the Megarean settlement.
After Constantine the Great made it the new eastern capital of the Roman Empire in 330 CE, the city became widely known as "Constantinopolis" (Constantinople), which, as the Latinized form of "" (Konstantinopolis), means the "City of Constantine". He also attempted to promote the name "Nova Roma" and its Greek version " " Nea Rom (New Rome), but this did not enter widespread usage. Constantinople remained the most common name for the city in the West until the establishment of the Turkish Republic, and Kostantiniyye (Ottoman Turkish: ) and Be Makam-e Qonstantiniyyah al-Mahmiyyah (meaning "the Protected Location of Constantinople") and stanbul were the names used alternatively by the Ottomans during their rule. The use of Constantinople to refer to the city during the Ottoman period (from the mid-15th century) is now considered politically incorrect, even if not historically inaccurate, by Turks.
By the 19th century, the city had acquired other names used by either foreigners or Turks. Europeans used Constantinople to refer to the whole of the city, but used the name Stamboulas the Turks also didto describe the walled peninsula between the Golden Horn and the Sea of Marmara. Pera (from the Greek word for "across") was used to describe the area between the Golden Horn and the Bosphorus, but Turks also used the name Beyolu (today the official name for one of the city's constituent districts). Islambol (meaning either "City of Islam" or "Full of Islam") was sometimes colloquially used to refer to the city, and was even engraved on some Ottoman coins, but the belief that it was the precursor to the present name, stanbul, is belied by the fact that the latter existed well before the former and even predates the Ottoman conquest of the city.
The name stanbul (Turkish pronunciation: [istanbu], colloquially [stambu]) is commonly held to derive from the Medieval Greek phrase " " (pronounced [is tim bolin]), which means "to the city" and is how Constantinople was referred to by the local Greeks. This reflected its status as the only major city in the vicinity. The importance of Constantinople in the Ottoman world was also reflected by its Ottoman name 'Der Saadet' meaning the 'gate to Prosperity' in Ottoman. An alternative view is that the name evolved directly from the name Constantinople, with the first and third syllables dropped. A Turkish folk etymology traces the name to Islam bol "plenty of Islam" because the city was called Islambol ("plenty of Islam") or Islambul ("find Islam") as the capital of the Islamic Ottoman Empire. It is first attested shortly after the conquest, and its invention was ascribed by some contemporary writers to Sultan Mehmed II himself. Some Ottoman sources of the 17th century, such as Evliya elebi, describe it as the common Turkish name of the time; between the late 17th and late 18th centuries, it was also in official use. The first use of the word "Islambol" on coinage was in 1703 (1115 AH) during the reign of Sultan Ahmed III. Nevertheless, the use of the name Constantinople remained common in English into the 20th century, Istanbul became common only after Turkey adapted the Latin alphabet in 1928 and urged other countries to use the city's Turkish name.
In modern Turkish, the name is written as stanbul, with a dotted , as the Turkish alphabet distinguishes between a dotted and dotless I. In English the stress is on the last syllable (bul), but in Turkish it is on the second syllable (tan). A person from the city is an stanbullu (plural: stanbullular), although Istanbulite is used in English.