The Yarmuk River (Arabic: نهر اليرموك, Nahr Al-Yarmuk, or شريعة المناذرة, Shariat el Menadhirah; Hebrew: נהר הירמוך, Nahar HaYarmukh; Latin: Hieromices), sometimes spelled Yarmouk, is the largest tributary of the Jordan River. It runs in Jordan, Syria, and Israel and drains much of the Hauran plateau. Its main tributaries are the ʾawdiya of 'Allan and Ruqqad from the north, Ehreir and Zeizun from the east. Although it is narrow and shallow throughout its course, at its mouth it is nearly as wide as the Jordan, measuring thirty feet in breadth and five in depth. The once celebrated Matthew Bridge used to cross the Yarmuk at its confluence with the Jordan.
The Yarmukian Culture is a Pottery Neolithic culture that inhabited parts of Palestine and Jordan. Its type site is at Sha'ar HaGolan, on the river mouth. Early Bronze Age I is represented in the Golan only in the area of the river.
Yarmuk forms a natural border between the plains to the north - Hauran, Bashan and Golan - and the Gilead mountains to the south. Thus it has often served as boundary line between political entities. The Aramean kingdoms and the Kingdom of Israel (Samaria), of the Hebrew bible, might have settled this way occasionally. Under the Assyrian and Persian empires the province of Ashteroth Karnaim laid to the north, and that of Gal'azu (Gilead) to the south. In Hellenistic times, the territory of Hippos was across from those of Gadara and Abila (Abel) on the south, while Dion sat on the eastern tributaries. Abila (Tel Abil) is attested in the 14th-century BC Amarna Letters. This is possibly the case also for Geshur, assumed to have laid north of the river. Other historical cities on the course of the river are Dara'a, Heet, Jalin; and the archaeological sites of Tell Shihab and Khirbet ed-Duweir (See Lo-debar).