JABBOK (Heb. יַבֹּק), tributary of the Jordan from the east, the first river south of the Yarmuk. The Hebrew name is derived either from the root meaning "to empty itself " or from a sound imitating the noise of water flowing over pebbles. The Jabbok is the confluent of three wadis: Wadi Amman, which rises near the city of Amman, Wadi Suwayliḥ, and Wadi al-Dhulayl. It flows at first in an easterly direction until the junction of the first two wadis, where it turns to the north. At the source of ʿAyn al-Zarqāʾ, from which the Arabic name of the river, Nahr al-Zarqāʾ, was derived, it becomes a perennial river. After joining Wadi al-Dhulayl it turns west and then southwest, watering the fertile plain of Succoth near the Jordan. It falls from approximately 2,489 ft. (758 m.) near Amman to approximately 1,684 ft. (513 m.) at Wadi al-Dhulayl and to approximately 1,149 ft. (513 m.) below sea level at the Jordan, dropping approximately 3,611 ft. (1,100 m.) in all over a total length of 43¾ mi. (70 km.). The drainage area is 1,015 sq. mi. (2600 sq. km.) and the annual discharge is 16 billion gallons (60 million cu. m.).
By cutting the mountains of Gilead into two, creating the two regions of the territory of Gilead, the Jabbok forms a natural boundary which served as a political border throughout almost all historical periods. The first biblical reference to the river occurs in connection with Jacob, who forded it on his way to meet Esau, following his departure from Haran (Gen. 32:23). His struggle with the angel took place at Peniel on a ford of the Jabbok, a place which was considered consecrated by later generations. The river is described as the northern boundary of the kingdom of Sihon the Amorite in Numbers 21:24 and Joshua 12:2. These passages apparently refer only to the lower reaches of the river, for the upper reaches were within the border of the Ammonites and were excluded from the area of the Israelite conquest (Deut. 2:37). Reuben and Gad inherited the lands of Sihon and thus the Jabbok also served as their border with Ammon (Deut. 3:16). Border disputes continued and in the time of Jephthah, the Ammonite kings claimed that the Israelite tribes had infringed upon their border (Judg. 11:13, 22). In later times the river served as the boundary of the land of the Tobiads. Eusebius describes it as the boundary of the cities of Gerasa and Philadelphia (Onom. 102:19ff.). According to a milestone placed beyond the Roman bridge built over the river, the territory of Gerasa extended slightly south of the Jabbok. In Arab times it served as the boundary between the districts of al-Balqāʾ and ʿAjlūn.
M.G. Ionides and T.S. Blake, Report on the Water Resources of Trans-Jordan (1939), passim; Maisler, Untersuchungen, 41–42; Abel, Geog, 1 (1933), 174–5, 485–6; Glueck, in: aasor, 25–28 (1951), 250–1, 313–8; EM, 3 (1965), 455–8.