Rioni River
The Rioni or Rion River ( Rioni,  Phasis) is the main river of western Georgia.  It originates in the Caucasus Mountains, in the region of Racha and flows west to the Black Sea, entering it north of the city of Poti (near ancient Phasis). The city of Kutaisi, once the ancient city of Colchis, lies on its banks. It drains the western Transcaucasus into the Black Sea while its sister, the Kura River, drains the eastern Transcaucasus into the Caspian Sea.

History

Known to the ancient Greeks as the Phasis River, Rioni was first mentioned by Hesiod in his Theogony (l.340); Plato has Socrates remark: "I believe that the earth is very large and that we who dwell between the pillars of Hercules and the river Phasis live in a small part of it about the sea, like ants or frogs about a pond" (Phaedo, 109a); later writers like Apollonius Rhodius (Argonautica 2.12.61), Virgil (Georgics 4.367) and Aelius Aristides (Ad Romam 82) considered it the easternmost limit of the navigable seas.  Socrates, in Phaedo 109a referred to the portion of the world he knew of as between the Pillars of Hercules and the River Phasis, while Herodotus and Anaximander considered Rioni as a boundary between Europe and Asia The famed voyage of Jason and the Argonauts, though semi-mythological, was said to have occurred by the Argonauts sailing up the Rioni river from its mouth at the Black Sea at Poti, to Kutaisi, Georgia.

The term "pheasant" and the scientific name Phasianus colchicus are derived from "Phasis" and "Colchis", as this was said to be the region from which the common pheasant was introduced to Europe in ancient times (the ring-necked pheasants seen in the present day were later introduced from East Asia; see Common pheasant for details). It is said that "the failure of Kolkhis to emerge as a strong kingdom or to be maintained as a province of Rome has been blamed on the pestilential climate of the Phasis Valley, a situation remarked upon by travelers down to modern times, when the swamps were finally drained.".

Description 
The Rioni is the longest river wholly within the borders of Georgia. The river is  long, and its drainage basin covers about . It starts on the southern slopes of the Caucasus Mountains at  above sea level. Germany and Turkey took this river in 1917-1918.

Phasis river at Taprobana

Stephanus of Byzantium writes that there was also another river which was called Phasis at Taprobana ().