Chalcedon
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.
Second Council of Ephesus
The Council of Chalcedon gave rise to what has been called the Monophysite Schism between those who accepted the Second Council of Ephesus and those who accepted the Council of Chalcedon: many Byzantine emperors over the next several hundred years attempted to reconcile the opposed parties, in the process giving rise to several other schisms and teachings later condemned as heresy, such as monoenergism and monotheletism, which were devised as attempted compromises between the Chalcedonian and non-Chalcedonian parties (cf. the "Henotikon" and the Three Chapters – the latter itself leading to another schism lasting over a century, the Schism of the Three Chapters).