Kassite, member of an ancient people known primarily for establishing the second, or middle, Babylonian dynasty; they were believed (perhaps wrongly) to have originated in the Zagros Mountains of Iran. First mentioned in Elamite texts of the late 3rd millennium bc, they penetrated into Mesopotamia in the 2nd millennium, were repulsed by Hammurabi’s son, but secured holdings within the Tigris-Euphrates valley on the northern frontiers of Babylonia and later established the second Babylonian dynasty. Chronicles and king lists are imprecise, and although the Kassite kings traditionally ruled over Babylonia for 576 years, it is probable that the first Kassite kings reigned in Babylonia simultaneously with the last kings of the first Babylonian dynasty; thus Gandash, the first Kassite king, possibly began his reign about the middle of the 18th century bc, but not at Babylon.
The Kassite kings appear to have been members of a small military aristocracy but were apparently efficient rulers and not locally unpopular. Their capital city was Dur-Kurigalzu. The horse, the sacred animal of the Kassites, probably first came into use in Babylonia at this time. Contemporary Kassite records are not numerous. Most belong to the archives of the guenna (provincial governor) of the city of Nippur and seem to indicate a feudal system of government during the 14th and 13th centuries.
One Kassite invention was the boundary stone (kudurru), a block of stone that served as a record of a grant of land by the king to favoured persons. The interest of the boundary stones for modern scholars is not only economic and religious but also artistic. The temples that the Kassite kings built or rebuilt are mainly in the Babylonian tradition, although one Kassite innovation was the use of molded bricks to form figures in relief.
In the 12th century Elam struck the final blow at Kassite power in Babylonia, already weakened by local insurrection. In the 1st millennium the Kassites withdrew to the Zagros Mountains, where they opposed the eastward expansion of Assyrian power and paid tribute to Persia. They were conquered by Alexander the Great but later regained their independence.