Chalcedon was founded by settlers from Megara on the Asian shore of the Bosphorus about seventeen years before the same people founded Byzantium on the European shore facing it. Herodotus reports a Persian commander's remark that the Chalcedonians must have been blind to choose their site when the better one lay in plain view across the water, and the phrase city of the blind stayed attached to the place in antiquity. It was a working Greek city for a thousand years, sacked repeatedly because it lay on the road every army took toward the straits, and by late antiquity its chief building was the martyrium of Saint Euphemia, a young woman executed under Diocletian whose shrine drew pilgrims from across the empire. That church, and the fact that the city stood within sight of the capital but outside its walls, is why the council of 451 met there rather than in Constantinople or at Nicaea, where it had first been summoned.
The site is now Kadikoy, a dense residential and commercial district on the Asian side of Istanbul, and nothing of the martyrium survives above ground; the relics were moved into the capital in the seventh century when the Persian wars made the Asian shore unsafe. Chalcedon also gave the Christian world one of its stranger stories. A tradition reported in later Greek sources holds that the two rival statements of faith were laid in the tomb of Euphemia and that, when it was opened, the orthodox one lay in her hands and the other at her feet, a legend that says more about how the council was remembered than about what happened in it.