The Mureș or Maros is a 789-kilometre-long (490 mi) river in Eastern Europe. Its drainage basin covers an area of 30,332 km2 (11,711 sq mi). It originates in the Hășmașu Mare Range in the Eastern Carpathian Mountains, Romania, rising close to the headwaters of the river Olt, and joins the Tisza at Szeged in southeastern Hungary. In Romania, its length is 761 km (473 mi) and its basin size is 27,890 km2 (10,770 sq mi).

The Olt is a river in Romania. It is 615 km (382 mi) long, and its basin area is 24,050 km2 (9,290 sq mi). It is the longest river flowing exclusively through Romania. Its average discharge at the mouth is 174 m3/s (6,100 cu ft/s). It originates in the Hășmaș Mountains of the eastern Carpathian Mountains, near Bălan, rising close to the headwaters of the river Mureș. The Olt flows through the Romanian counties of Harghita, Covasna, Brașov, Sibiu, Vâlcea, and Olt. The river was known as Alutus or Aluta in Roman antiquity. Olt County and the historical province of Oltenia are named after the river.