Most important cities and empires do have origins that are shrouded in mystery and the origins of Byzantium is no exception. Centuries before the Eastern Roman capital Constantinople was founded (330), the settlement of Byzantium that had predated Constantinople in the same location is said to have dated back to the 7th century BC starting as an Ancient Greek colony. Although different accounts tell different stories of Byzantium's legendary founding, the one we will go with is the version of Byzas of Megara as its founder mentioned in the 6th century "Patria of Constantinople" in which Byzas' origins are also shrouded in mystery as some say he is the son of the Greek god Poseidon and related to the other Greek gods as well while others say he is the son of the King of Megara Nisos.
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In this case with Byzas being the son of Nisos who after consulting with the Oracle of Delphi who told him to set up a colony for Megara in the "land opposite of the city of the blind", he sent Byzas by ship to search for it. After sailing north up the Aegean Sea from Megara which was near Athens, Byzas and his Megarian colonists arrived where the Marmara Sea (Propontis) narrows into the Bosporus on the border of Europe and Asia. Byzas now concluded here that the existing Greek settlement (Chalcedon) on the Asian side of the Bosporus was the "land of the blind", thus he chose to settle and build a colony in the peninsula across it which eventually grew into the Megarian Greek colony of Byzantium (Byzantion) named after Byzas.
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When establishing his colony there, Byzas later married the daughter of a nearby Thracian king to make peace with these Thracians, although the date of Byzas' death remains unclear. Eventually, Byzas' colony would evidently prove to be at a perfect spot and was a better choice than Chalcedon, and this was because Byzantium commanded the entrance to two seas (Black and Marmara) while those in Chalcedon were called "blind" as the location they chose was not strategic compared to Byzantium.
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Without much images online of Byzas, I chose to draw him here depicting him as an Ancient Greek hoplite.
Art by Powee Celdran, 2022