- Tribes are groups of people who share customs and language and the belief that they descend from a common ancestor. The best evidence for the social organization of ancient tribes comes from the archive of Mari, a city of the Middle Euphrates, which was surrounded by tribal populations. Some tribes were predominantly pastoralists and moved with their herds of sheep and goats according to available pasture and were essentially nomads. Other tribes chose more sedentary modes of life and combined herding with agriculture. The authority to settle disputes rested with a patriarchal leader, or sheikh, who ruled on a consensual basis.Tribal groups are often described as causing problems for cities and their hinterland by encroaching on land, destroying crops, and damaging irrigation works. Large waves of immigration from tribal areas, especially the West and East, could cause the general breakdown of central control, and neither military expeditions nor the building of walls to keep them out proved effective in the long run. The pattern throughout Mesopotamian history was a mutually beneficial coexistence of urban populations and tribal people, especially in the regions of Assyria and northern Babylonia, and of large-scale tribal immigration that, after initial destabilization, would result in the absorption of significant numbers of tribal people and their elites into the urban population.
Historical Dictionary of Mesopotamia. EdwART. 2012.