Galbert of Bruges (2013). The Murder, Betrayal, and Slaughter of the Glorious Charles, Count of Flanders. Translated by Rider, Jeff. Yale University Press.
Houben, Hubert (2002). Roger II of Sicily: A Ruler Between East and West. Cambridge University Press.
Brandenburg, E. (1998). Die Nachkommen Karls des Großen (ภาษาGerman). Neustadt an der Aisch.CS1 maint: unrecognized language (link)
