See:
- William Matthew Flinders Petrie, James Edward Quibell: Naqada and Ballas. London 1896, p. 65, Pl. Ia, LXXXV- https://ia600205.us.archive.org/17/items/cu31924028748261/cu31924028748261.pdf
- Andrzej Ćwiek. "Date and Function of the so-called Minor Step Pyramids." Göttinger Miszellen Vol. 162, Göttingen 1998, pp. 39–52.