The Nahr al-Kabir, also known in Syria as al-Nahr al-Kabir al-Janoubi (, in contrast with the Nahr al-Kabir al-Shamali) or in Lebanon simply as the Kebir, is a river in Syria and Lebanon flowing into the Mediterranean Sea at Arida. The river is 77.8 km long, and drains a watershed of 954 km2. Its headwaters are at the Ain as-Safa spring in Lebanon and it flows through the Homs Gap in the Orontes River Valley of southern Syria. The river forms the northern part of the Lebanon–Syria border. In antiquity, the river was known as Eleutherus (Greek Ελεύθερος Eleutheros, Ελευθερίς Eleuteris lit. 'free'). It defined the border between the Seleucid and Ptolemaic empires during much of the 3rd century BCE. The river is mentioned by Josephus and in 1 Maccabees 11:7 and 12:30.