According to Pliny the Elder in his Natural History, the first known name of a settlement on the site of Constantinople was Lygos, a settlement likely of Thracian origin founded between the 13th and 11th centuries BC. The site, according to the founding myth of the city, was abandoned by the time Greek settlers from the city-state of Megara founded Byzantium (Ancient Greek: Βυζάντιον, Byzántion) in around 657 BC, across from the town of Chalcedon on the Asiatic side of the Bosphorus.
The origins of the name of Byzantion, more commonly known by the later Latin Byzantium, are not entirely clear, though some suggest it is of Thraco-Illyrian origin. The founding myth of the city has it told that the settlement was named after the leader of the Megarian colonists, Byzas. The later Byzantines of Constantinople themselves would maintain that the city was named in honour of two men, Byzas and Antes, though this was more likely just a play on the word Byzantion.
The city was briefly renamed Augusta Antonina in the early 3rd century AD by the Emperor Septimius Severus (193–211), having razed the city to the ground in 196 for supporting a rival contender in the civil war and rebuilt, in honour of his son Antoninus, the later Emperor Caracalla. The name appears to have been quickly forgotten and abandoned, and the city reverted to Byzantium/Byzantion after either the assassination of Caracalla in 217 or, at the latest, the fall of the Severan dynasty in 235.
Names of Constantinople
Byzantium took on the name of Kōnstantinoupolis ("city of Constantine", Constantinople) after its refoundation under Roman emperor Constantine I, who transferred the capital of the Roman Empire to Byzantium in 330 and designated his new capital officially as Nova Roma (Νέα Ῥώμη) 'New Rome'. During this time, the city was also called 'Second Rome', 'Eastern Rome', and Roma Constantinopolitana. As the city became the sole remaining capital of the Roman Empire after the fall of the West, and its wealth, population, and influence grew, the city also came to have a multitude of nicknames.
As the largest and wealthiest city in Europe during the 4th–13th centuries and a centre of culture and education of the Mediterranean basin, Constantinople came to be known by prestigious titles such as Basileuousa (Queen of Cities) and Megalopolis (the Great City) and was, in colloquial speech, commonly referred to as just Polis (ἡ Πόλις) 'the City' by Constantinopolitans and provincial Byzantines alike.
In the language of other peoples, Constantinople was referred to just as reverently. The medieval Vikings, who had contacts with the empire through their expansion in eastern Europe (Varangians) used the Old Norse name Miklagarðr (from mikill 'big' and garðr 'city'), and later Miklagard and Miklagarth. In Arabic, the city was sometimes called Rūmiyyat al-Kubra (Great City of the Romans) and in Persian as Takht-e Rum (Throne of the Romans).
In East and South Slavic languages, including in medieval Russia, Constantinople has been referred to as Tsargrad (Царьград) or Carigrad, 'City of the Caesar (Emperor)', from the Slavonic words tsar ('Caesar' or 'King') and grad ('city'). This was presumably a calque on a Greek phrase such as Βασιλέως Πόλις (Vasileos Polis), 'the city of the emperor [king]'.
Modern names of the city
The modern Turkish name for the city, İstanbul, derives from the Greek phrase eis tin polin (εἰς τὴν πόλιν), meaning "(in)to the city". This name was used in Turkish alongside Kostantiniyye, the more formal adaptation of the original Constantinople, during the period of Ottoman rule, while western languages mostly continued to refer to the city as Constantinople until the early 20th century. In 1928, the Turkish alphabet was changed from Arabic script to Latin script. After that, as part of the 1920s Turkification movement, Turkey started to urge other countries to use Turkish names for Turkish cities, instead of other transliterations to Latin script that had been used in Ottoman times. In time the city came to be known as Istanbul and its variations in most world languages.
The name "Constantinople" is still used by members of the Eastern Orthodox Church in the title of one of their most important leaders, the Orthodox patriarch based in the city, referred to as "His Most Divine All-Holiness the Archbishop of Constantinople New Rome and Ecumenical Patriarch." In Greece today, the city is still called Konstantinoúpoli(s) (Κωνσταντινούπολις/Κωνσταντινούπολη) or simply just "the City" (Η Πόλη).