The Axios ( Greek: Αξιός , is the longest river in the FYROM. It is 388 kilometres long, and drains an area of around 25,000 km².
The river begins at Vrutok, a few kilometers north of Tetovo in the FYROM. It passes through Skopje and into Veles, crosses the Greek border near Gevgeli, Polykastro and Axioupolis ("town on the Axios"), before flowing into the Aegean Sea in Central Macedonia west of Thessaloniki in northern Greece.
The Vardar basin includes 80% of the territory of the FYROM. The valley comprises fertile lands in the Kilkis and Thessaloniki prefectures and Gevgeli and other parts. The river is surrounded by mountains elsewhere. The superhighways Greece Interstate 1 in Greece and M1 and E75 run within the valley along the river's entire length to near Skopje.
The river valley has given its name to the vardaris, a northerly prevailing ravine wind which blows down the length of the valley to bring cold conditions to the Thessaloniki area of Greece. It occurs when atmospheric pressure over eastern Europe is higher than over the Aegean Sea, as is often the case in winter. It is somewhat similar to the mistral wind of France.