In the Aeneid, Halys is a Trojan who defends Aeneas' camp from a Rutullian attack.

The Halys is the ancient Greek name for the longest river in Turkey, where it is known as Kızılırmak ("Red River"). The Hittites called it the Marassantiya River.

The Halys flows about 1 150 kilometers from the central Turkish plateau, first to the southwest, then to the north and northeast into the Black Sea. Although it is not used for navigation, it is a source of hydroelectric power. Its major tributary is the Delice Irmak, also known by its Greek name Cappadox .

In the ancient world it was the boundary between Asia Minor and the rest of Asia. It was the border between Lydia and Persia until Croesus of Lydia crossed it to attack Cyrus the Great in 547 BC; he was defeated (see Battle of Halys ) and Persia expanded to the Aegean Sea.