It is formed by the confluence of the Seil es-Sufej with the Wadi el-Muğireş; near its mouth it receives on the right the tributaries Seil Heidän and Seil en-Nimr. It flows through a picturesque gorge in reddish rock, up to 650 m deep. Its waters abound with fish.
The A. marked the boundary between the territory of the Amorites (v.) with capital Hesebon, later of the Ammonites (v.), to the north, and that of the Moabites, to the south (Num. 21:13-15; 22:36; Mesha inscription, line 26); later it constituted the southern limit of the tribe of Reuben (Jos. 13:9, 16), i.e., of the trans-Jordanian Israelite territory (Deut. 3:12; 4:48).
BIBL.: F.-M. Abel, Géographie de la Palestine, I, Paris 1933, pp. 177 ff., 487 ff.; id., Une croisière autour de la Mer Morte, Paris 1911, pp. 46-52.