Vardar. The Vardar or Axios is the longest river in North Macedonia and a major river in Greece, where it reaches the Aegean Sea at Thessaloniki. It is 388??km (241??mi) long, out of which 76??km (47??mi) are in Greece, and drains an area of around 25,000??km2 (9,653??sq??mi). The maximum depth of the river is 4??m (13??ft).