The Rioni River is the principal river of western Georgia. It originates in the Caucasus Mountains, in the region of Racha and flows west to the Black Sea. It enters the Black Sea north of the city of Poti. The city of Kutaisi, once the capital of ancient Colchis, lies on its banks.

Known to the ancient Greeks as the Phasis River, it was first mentioned by Hesiod in his Theogony (l.340); later writers like Apollonius Rhodius (Argonautica 2.12.61), Vergil (Georgics 4.367) and Aelius Aristides (Ad Romam 82) considered it the easternmost limit of the navigatible seas.