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.
Ecthesis
By the beginning of the 7th century, the court and the religious hierarchy at Constantinople were by and large firmly in the Chalcedonian camp. However, this put them at odds with the majority Non-Chalcedonians in Egypt, Syria, Mesopotamia and Armenia. Such a division was dangerous in an empire that was under threat from the Persian Sassanids, especially as the Non-Chalcedonians considered their schismatic brethren to be more of a threat than any foreign invader. Consequently, the emperors at Constantinople were always seeking some method of rapprochement to heal the breach in the church, and thereby prevent the empire’s enemies from taking advantage of the internal divisions.