The Flemish Succession Crisis: Robert the Frisian vs. Richilde and Arnulf III (1067–1071)

Following the death of Baldwin VI of Flanders in 1070, a succession crisis erupted, pitting Robert the Frisian, Baldwin’s younger brother, against Richilde of Hainaut, Baldwin’s widow and regent for their young son, Arnulf III. The conflict would draw in France, Normandy, and other regional powers, culminating in a major battle for control of Flanders.

Robert the Frisian’s Background and Early Career

• Robert was the younger son of Baldwin V of Flanders and Adèle of France, making him the brother of Baldwin VI and the brother-in-law of William the Conqueror through their sister, Queen Matilda of England.
• In 1063, Robert had married Gertrude of Saxony, the widow of Floris I, Count of Holland, becoming stepfather to Dirk V, Count of Holland.
• His nickname, "the Frisian," stemmed from his role as regent for Dirk V, as Holland was then commonly referred to as Frisia.

Baldwin VI’s Succession Plan and Robert’s Betrayal (1067–1070)

• On his deathbed in 1067, Baldwin VI entrusted Flanders to his son, Arnulf III, with Hainaut assigned to his younger son, Baldwin II.
• Baldwin also made Robert the guardian of Arnulf, expecting him to protect his young nephew’s inheritance.
• However, Robert soon betrayed this agreement, rejecting his oath of homage and invading Ghent in 1070, declaring himself Count of Flanders.

Richilde Appeals to France and Normandy (1070–1071)

• Richilde of Hainaut, Arnulf’s mother, sought aid from King Philip I of France, who summoned Robert to appear before him.
• Robert refused, instead continuing his military campaign to claim Flanders for himself.
• In response, Philip I led an army into Flanders, aiming to restore Arnulf III’s rule.
• Richilde secured further military support from Normandy, with Queen Matilda (Robert’s sister) sending Norman knights to support Philip I and Arnulf III.
• The Norman forces were led by William FitzOsbern, a trusted ally of William the Conqueror, who had also accepted a marriage proposal from Richilde.

The War for Flanders: The Road to Cassel (1071)

• The confrontation between Robert and Richilde’s forces, now backed by France and Normandy, would culminate in the Battle of Cassel (1071).
• Count Eustace II of Boulogne and other pro-Capetian nobles also joined Arnulf’s side, making this a significant war over Flemish succession.
• The outcome of the battle would determine the future ruler of Flanders, deciding whether Baldwin VI’s son or his brother Robert would control the county.

The Flemish succession war (1070–1071) was one of the most significant power struggles of 11th-century France, shaping the political future of Flanders and its relationship with both France and Normandy.