Sesostris I (sĭsŏsˈtrĭs) [key], d. 1926 B.C., king of ancient Egypt, 2d ruler of the XII dynasty; son and successor of Amenemhet I. He was coregent with his father from 1980 B.C.; from 1971 to 1926 he was sole ruler. His reign was notable for successful campaigns in Nubia. Sesostris' son and successor, Amenemhet II, was his coregent during the last three years of his reign.
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