Bakırçay (Latin: Caicus, Ancient Greek: Κάϊκος) is a river in Turkey.

The Kaikos River is mentioned by Hesiod[1] and Plutarch, who claims that its name was originally Astraeus (Ἀστραῖος) but was changed after Caicus, a son of Hermes, threw himself into it after sleeping with his sister Alcippe.

[2] However, since the course of the river has changed since antiquity it is not clear how the ancient names apply to the modern geographical features.

Leake infers from the direction of L. Scipio's march from Troy to the Hyrcanian plain, that the Caicus was the north-eastern branch of the river of Pergamon which flows by Menduria (possibly Gergitha) and Balıkesir (Caesaraea).

[3] The Caicus as it seems is formed by two streams which meet between 50 and 65 km above its mouth, and it drains an extensive and fertile country.