Sesostris II (sĭsŏsˈtrĭs) [key], d. 1878 B.C., king of ancient Egypt, of the XII dynasty. He was the son of Amenemhet II, first his coregent (1900 B.C.), then his successor (1897–1878). His son Sesostris III succeeded him. d. 1840 B.C., succeeded (1878 B.C.) his father Sesostris II. He fixed the southern boundary of Egypt above the Second Cataract of the Nile not far from Wadi Halfa and curbed the power of the Egyptian nobles.