Robert I of Flanders defeated his nephew Arnulf III to secure control of Flanders, reshaping the county's succession and regional power balance in northern Europe.
Key Facts
- Date
- February 28, 1071
- Victor
- Robert I of Flanders (Robert the Frisian)
- Arnulf III's fate
- Killed in battle
- Notable casualty
- William FitzOsbern, Norman commander
- Richilde's fate
- Captured, later exchanged for Robert's freedom
- Robert's rule
- Became Count of Flanders, ruled until 1093
Location
Cause → Event → Consequence
When Baldwin VI of Flanders died in 1070, his young son Arnulf III succeeded him, supported by his mother Richilde and King Philip I of France. Robert I, Baldwin's brother, disputed the succession and gathered support primarily in northern Flanders, where Arnulf's forces were concentrated, setting the stage for armed conflict.
Robert I's forces attacked Arnulf III's numerically superior but disorganized army near Cassel in February 1071. Arnulf III and Norman commander William FitzOsbern were killed in the fighting. Richilde was captured by Robert's forces, while Robert himself was briefly captured by Eustace II of Boulogne before being released in exchange for Richilde.
Robert I secured the County of Flanders and ruled until 1093. He reconciled with King Philip I of France by arranging the king's marriage to his stepdaughter, Bertha of Holland, converting a former adversary into an ally and stabilizing his position as count.
Belligerents & Mobilization Analysis
Side A
1 belligerent
Robert I of Flanders.
Side B
1 belligerent
Arnulf III of Flanders, Richilde of Hainaut, Eustace II of Boulogne, William FitzOsbern.