Neolithic artifacts, dating back to the 7th millennium BC and uncovered by archaeologists at the beginning of the 21st century AD, indicate Istanbul's historic peninsula was settled earlier than previously thought and before the Bosphorus was even formed. Before the discovery, conventional wisdom held that Thraciantribes, including the Phrygians, began settling on the Sarayburnu in the late-6th millennium BC. On the Asian side, artifacts originating around the 4th millennium BC have been found in Fikirtepe (withinKadıköy). The same location was the site of aPhoenician trading post at the beginning of the 1st millennium BC as well as the town of Chalcedon, which was established in c. 680 BC.
However, the history of Istanbul generally begins around 660 BC, when settlers from Megara, under the command of King Byzas, established Byzantium on the European side of the Bosphorus. The settlers proceeded to build an acropolis adjacent to the Golden Horn on the site of the early Thracian settlements, fueling the nascent city's economy. The city experienced a brief period ofPersian 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, theSecond Athenian Empire, before ultimately gaining independence in 355 BC. Long allied with the Romans, Byzantium officially became a part of the Roman Empire in 73 AD.
Byzantium's decision to side with the usurper Pescennius Niger against Roman Emperor Septimius Severus cost it dearly; by the time it surrendered at the end of 195 AD, 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
