The Halys is the ancient Greek name for the longest river in Turkey, where it is known as Kızılırmak ("Red River"). It is not used for navigation, but a source of hydroelectric power.

The Halys flows for a total of about 1,150 kilometers, rising in the eastern Anatolian highlands around , flowing first to the west and south-west until , then forming a wide arch, flowing first to the west, then to the north-west, passing to the north-east of Lake Tuz, then to the north and northeast where it is joined by its major tributary, the Delice Irmak (also known by its Greek name Cappadox) at , and after zig-zagging to the north-west to the confluence with the Devrez River at , and back to the north-east finally empties into the Black Sea at .

The Hittites called it the Marassantiya River. It formed the boundary of the land Hatti, the core land of the Hittite Empire. In the Classical Antiquity it was the boundary between Asia Minor and the rest of Asia. As the site of the Battle of the Eclipse in 585 BC, 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.

Rivers of Turkey

Kızılırmak | Kızılırmak | Halys | Kizil Irmak | クズルウルマク川 | Kızılırmak | Kızılırmak | Kızılırmak