Bells in the shape of truncated pyramids are associated with the Benin kingdom of southern Nigeria. Of the 895 Benin brass plaques documented by Philip Dark, 132 have such bells represented on them, usually suspended on the chests of chiefs or retainers. The bells are thought to be an indicator of military rank and to protect warriors from danger. They are also placed on ancestral altars.
Source: DjeDje, J. C. (1999). “Turn Up the Volume! A Celebration of African Music”, Los Angeles: UCLA Fowler Museum of Cultural History. page 273