He defeated the army of Flanders that had invaded Walcheren in 1253, where he captured Guy and John of Dampierre, both sons of Margaret II, Countess of Flanders and commanders for Flanders. In 1256 he signed a peace treaty (called the "Treaty of Péronne") with Flanders on the status of Zeeland, reaffirming Flanders' rights west of the Scheldt river. Flanders was forced to compensate Holland for the damages of the war and only after this Margaretha's sons were freed. Floris was killed at a tournament in Antwerp, and was buried in Middelburg.Historical notes on Holland
