Chalcedon (
/kælˈsiːdən/ or /ˈkælsɨdɒn/;Greek: Χαλκηδών, sometimes transliterated as Chalkedon) was an ancient maritime town of Bithynia, in Asia Minor, almost directly opposite Byzantium, south of Scutari (modern Üsküdar). It is now a district of the city of Istanbul named Kadıköy. The name is a variant of Calchedon (Greek: Καλχήδων), found on all the coins of Chalcedon as well as in manuscripts of Herodotus's Histories, Xenophon's Hellenica, Arrian's Anabasis, and other works. Almost no aboveground 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. A stream, called the Chalcis or Chalcedon in antiquity and now known as the Kurbağalıdere (Turkish: stream with frogs), flows into Fenerbahçe bay. There Greek colonists from Megara in Attica founded the settlement of Chalcedon in 685 BC, some seventeen years before Byzantium.