Origins
The name 'Constantinople' is a transparent Greek compound: 'Kōnstantinos' (Κωνσταντῖνος, the name Constantine) + 'polis' (πόλις, city) = 'the city of Constantine.' It follows a name-formation pattern common in the Greek world, where cities were named for their founders or patrons by adding '-polis' to a personal name.
The city was founded — or more precisely, refounded — by the Roman Emperor Constantine I (r. 306-337 CE) in 330 CE. The site was not new: the ancient Greek city of Byzantion (Βυζάντιον, Latinized as Byzantium) had stood on the same spot since its founding by Greek colonists from Megara around 657 BCE. But Constantine chose this location — at the crossroads of Europe and Asia, commanding the Bosporus strait and the route between the Mediterranean and the Black Sea — as the site for a 'New Rome,' a new capital for the Roman Empire. He renamed it after himself: Konstantinoupolis.
Constantinople served as the capital of the Roman Empire (later called the Byzantine Empire by modern historians) for over eleven centuries, from 330 to 1453 CE. For most of that period, it was the largest, wealthiest, and most culturally sophisticated city in Europe and the Mediterranean world. Its population reached half a million or more at its peak — dwarfing any Western European city of the same era. The Hagia Sophia, built by Emperor Justinian in 537 CE, was the largest cathedral in the world for nearly a thousand years.
Greek Origins
In the Greek-speaking world, Constantinople was often referred to simply as 'hē Polis' (ἡ Πόλις, 'the City') — the definite article indicating that it was the city, the one that needed no further identification. This usage is significant for the history of the word 'polis' itself: Constantinople was so supreme that the common noun 'city' functioned as its proper name.
The modern name 'Istanbul' has a debated etymology, but the most widely accepted scholarly explanation derives it from Medieval Greek 'eis tēn Polin' (εἰς τὴν Πόλιν, 'to the City' or 'into the City'). Greek speakers traveling to Constantinople would say they were going 'eis tēn Polin' — to the City. Turkish speakers adapted this phrase into 'Istanbul.' If this etymology is correct, then the name 'Istanbul' itself contains the Greek word 'polis' in its accusative form — a remarkable survival.
The city was conquered by the Ottoman Sultan Mehmed II on May 29, 1453, ending the Byzantine Empire. The Ottomans made it their capital, and it remained the capital of the Ottoman Empire until its dissolution in 1922. The name 'Constantinople' continued in international use alongside Turkish names until 1930, when the Turkish government formally adopted 'Istanbul' as the city's sole official name.
Latin Roots
The '-polis' element in 'Constantinople' connects it to the rich vocabulary of Greek city-words: metropolis (mother city), acropolis (high city), necropolis (city of the dead), megalopolis (great city), and the concept of the 'cosmopolitan' (citizen of the world). Constantinople, as the greatest city of the medieval world, embodied all these categories: it was the mother city of Orthodox Christianity, a city on a high promontory, a city with vast necropolises, a city of megalopolitan scale, and above all a cosmopolitan crossroads where Greek, Roman, Persian, Arab, Slavic, and Western European cultures met and mixed.