Sennar (sĕnärˈ) [key] or Sannar sänärˈ, town, SE Sudan, on the Blue Nile. It was the capital of the Muslim kingdom of Sennar, traditionally known as the "Black Sultanate," which was founded in the 16th cent. Under its strongest rulers, Sennar extended over most of the eastern part of the present Sudan. The kingdom declined in the 18th cent. and was annexed in 1821 by Egypt, then a part of the Ottoman Empire. The old capital lies abandoned near modern Sennar. The Sennar Dam, completed in 1925, is used for crop irrigation.