Beeler, John (1971). Warfare in Feudal Europe, 730-1200. Cornell University Press. For example, the two modern historians who have written in detail about the rather obscure battle of Cassel in Flanders (22 February 1071)...

Douglas, David Charles (1967). William the Conqueror: The Norman Impact Upon England. University of California Press. The decisive battle was fought on 22 February 1071, and it resulted in the overthrow of Richeldis, the establishment of Robert le Frison as count of Flanders....

France, John (1994). Victory in the East: A Military History of the First Crusade. Cambridge University Press.  0-521-58987-8. The battle of Cassel on 22 February 1071 was fairly widely noted by contemporaries . ... Arnulf III was killed and so was William FitzOsborn ; Richilde was captured by Robert's men..

ISBN

Hagger, Mark (2012). William: King and Conqueror. I.B. Tauris.

Oksanen, Eljas (2012). Flanders and the Anglo-Norman World, 1066–1216. Cambridge University Press.

Rex, Peter (2011). 1066: A New History of the Norman Conquest. Amberley Publishing.