Recent construction of the Marmaray tunnel unearthed a Neolithic settlement underneath Yenikap 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 Topkap Palace now stands, between the 13th and 11th centuries BC. On the Asian side, artifacts have been found in Fikirtepe (present-day Kadköy) 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 BCE.[11]
However, the history of Istanbul generally begins around 660 BCE,[note 1] 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 BCE. 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.