Kadıköy is an older settlement than most of those on the Asian side of the city of İstanbul. Relics dating to 5500-3500 BC (Chalcolithic period) have been found at the FikirtepeMound, and articles of stone, bone, ceramic, jewelry and bronze show that there has been a continuous settlement since prehistoric times. A port settlement dating from thePhoenicians has also been discovered. Chalcedon was the first settlement which the Greeks from Megara established on the Bosphorus, in 685 BC, a few years before they established Byzantium on the other side of the strait in 667 BC. Chalcedon became known as the 'city of the blind', the story being that Byzantium was founded following a prophecy that a great capital would be built 'opposite the city of the blind' (meaning that the people of Chalcedon must have been blind not to see the obvious value of the peninsula on the Golden Horn as a natural defensive harbour). Chalcedon changed hands time and time again, as Persians,Bithynians, Romans, Byzantines, Arabs, Crusaders, and Turks passed through the area, which was badly damaged during the Fourth Crusade and came into Ottoman hands in 1353, a full century before Constantinople. Thus, Kadıköy has the oldest mosque in İstanbul, built almost a century before the conquest of Constantinople in 1453.
At the time of the conquest, Chalcedon was a rural settlement outside the protection of the city. It was soon put under the jurisdiction of the Constantinople courts, hence the name Kadıköy, which means Village of the Judge. In the Ottoman period, Kadıköy became a popular market for agricultural goods and in time developed into a residential area for people who would commute to the city by boat. The population was the typical Ottoman Constantinople mix of Armenians,Greeks, Jews and Turks. Kadıköy has several churches (Greek, Armenian, Serbian, Catholic,Protestant) and synagogues