'''Halkedon''' (Χαλκεδον, ''Chalkedon'', na [[turski jezik|truskom]], [[Kadikoy|Kadıköy]]
, ) bio je stari pomorski grad u [[Bitinija|Bitiniji]], u [[Mala Azija|Maloj Aziji]], skoro nasuprot [[Bizantijum]]u; danas je to moderna četvrt u azijskom dijelu [[Istanbul]]a, južno od četvrti [[Üsküdar (Istanbul)|Üsküdar]] (stari Skutari).
In its early history it shared the fortunes of Byzantium, was taken by the [[satrap]] Otanes, vacillated long between the [[Sparta|Lacedaemonian]] and the [[Athens|Athenian]] interests, and was at last bequeathed to the [[Roman Republic]] by [[Attalus III]] of [[Pergamum]] ([[133 BC|133 b.c.]]).
It was partly destroyed by [[Mithradates]], but recovered during the Empire, and in [] CE was the location of the [[Council of Chalcedon]].
It fell under the repeated attacks of the [[barbarian]] hordes who crossed over after having ravaged Byzantium, and furnished an encampment to the [[Persian Empire|Persians]] under [[Khosrau I of Persia|Chosroes]], c. []-[]. The [[Ottoman Turks|Turks]] used it as a quarry for building materials for [[Constantinople]].
To the south are the ruins of [[Panteichion]] (mod. Pendik), where [[Belisarius]] is said to have lived in retirement.
The name of the mineral [[chalcedony]] is derived from that of this town.
It is today [[Kadikoy|Kadıköy]], a district of [[Istanbul]], [[Turkey]].