Sesostris ISesostris I - While Egypt's Old Kingdom is well-known for its building projects and the New Kingdom is known for its expansionist tendencies and powerful pharaohs, the Middle Kingdom is not well-known for much of anything (kind of like the neglected middle child of the family). However, that is not to say that the Middle Kingdom did not have its important contributions. One of the most important rulers was Sesostris I, the second pharaoh of the 12th Dynasty. He had a long and prosperous reign, ca. 1971-1926 BC, was a prodigious builder and conducted several military campaigns against Libya and Nubia to expand Egypt's borders to the west and south.