Battle of Cassel

On February 22, 1071, on the heights of Cassel, Robert the Frisian faced the army of his nephew Arnoul III supported by Richilde of Hainaut, by King Philip I and by imperial contingents. After several hours of fierce melee, Robert managed to break through the opposing vanguard, took Count Eustache de Boulogne prisoner and killed Arnoul himself, causing the rout of the loyalist party. Aftermath: Philip recognises Robert as count (homage); 1072 marriage to Bertha of Holland, Robert’s stepdaughter; Richilde defeated at Broqueroie 1072 (French Wikipedia).

On the death of Baldwin VI of Flanders, the regency of his minor son Arnoul III was contested by Robert the Frisian, brother of the deceased, who benefited from the support of the Flemish maritime cities. Richilde seeks the support of the King of France and the Holy Roman Empire, bringing together in Cassel a composite army mixing Hennuyer knights, Picards and royal troops. Robert relies on the urban militia of Bruges, on seasoned Flemish knights and on an excellent knowledge of the hills of Cassel. Aftermath: Philip recognises Robert as count (homage); 1072 marriage to Bertha of Holland, Robert’s stepdaughter; Richilde defeated at Broqueroie 1072 (French Wikipedia).

Robert the Frisian held the height of Cassel; Philip I's royal army, the larger force, camped at Bavinchove. Robert attacked at once, before it could deploy, and the fighting lasted all day. Arnulf III was killed there, as were William FitzOsbern with about ten Norman knights, and Anselm of Ribemont. The captures crossed over: Robert seized Richilde, while Eustace of Boulogne captured Robert himself; the two prisoners were later exchanged at Saint-Omer.

The death of Arnoul and the temporary capture of Richilde put an end to the war of succession: Robert was recognized as Count of Flanders after having negotiated the release of King Philip I, injured and captured in the melee. The new balance consolidates Flemish autonomy while forcing Robert to come to terms with the Capetian royalty, whose ally he becomes against imperial incursions. The Flemish towns gain an interlocutor favorable to their privileges. Aftermath: Philip recognises Robert as count (homage); 1072 marriage to Bertha of Holland, Robert’s stepdaughter; Richilde defeated at Broqueroie 1072 (French Wikipedia).