It was located almost directly opposite Byzantium, south of Scutari (modern Üsküdar) and it is now a district of the city of Istanbul named Kadıköy.

The name Chalcedon is a variant of Calchedon, found on all the coins of the town as well as in manuscripts of Herodotus's Histories, Xenophon's Hellenica, Arrian's Anabasis, and other works.

Except for the Maiden's Tower, almost no above-ground vestiges of the ancient city survive in Kadıköy today; artifacts uncovered at Altıyol and other excavation sites are on display at the Istanbul Archaeological Museum.

The site of Chalcedon is located on a small peninsula on the north coast of the Sea of Marmara, near the mouth of the Bosphorus.

There, Greek colonists from Megara in Attica founded the settlement of Chalcedon in 685 BC, some seventeen years before Byzantium.

[4] The mound of Fikirtepe has yielded remains dating to the Chalcolithic period (5500–3500 BC) and attest to a continuous settlement since prehistoric times.

The colonists from Megara settled on a site that was viewed in antiquity as so obviously inferior to that visible on the opposite shore of the Bosphorus (with its small settlements of Lygos and Semistra on Seraglio Point), that the 6th-century BC Persian general Megabazus allegedly remarked that Chalcedon's founders must have been blind.

[7][8] Nevertheless, trade thrived in Chalcedon; the town flourished and built many temples, including one to Apollo, which had an oracle.

Darius the Great's bridge of boats, built in 512 BC for his Scythian campaign, extended from Chalcedonia to Thrace.

There is a list of its bishops in Le Quien,[16] completed by Anthimus Alexoudes,[17] revised for the early period by Pargoire.