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.
Sarayburnu
According to a legend, in 667 BC ancient Greek settlers from Megara (near Athens) under the command of King Byzas established Byzantium at the Sarayburnu. Previously, in 685 BC, the Megarans had established Chalcedon (present-day Kadıköy) on the Anatolian shore, across the Bosporus. Actually the oldest settlements in present-day Istanbul are found on the Anatolian side; such as the Fikirtepe mound which dates from the Chalcolithic period (Copper Age), with artifacts dating from 5500-3500 BC. In nearby Kadıköy (ancient Chalcedon), a large port settlement dating from the Phoenicians (which predates the Megaran settlement) has been discovered.