Why is July 11th a national holiday in Flanders/Belgium?

HISTORY OF DAY OF THE FLEMISH COMMUNITY
The holiday dates back to 1302 when Flemish citizens of the city Bruges rebelled against the French king, Phillip IV, and attacked the French governors of Flanders. Consequently, the enraged king sent an army consisting of 2,500 knights and squires, along with the support of 5,000 infantry, to punish the Flemish citizens.

In an open field outside the Flemish city of Kortrijk (Courtrai), the army of the king and 9,000 Flemish militia (an army of non-professional civilian soldiers), consisting mainly of infantry, clashed on July 11 in a seemingly one-sided battle. Anybody would think that the massive army of soldiers of the French king would have easily defeated the town militia.

But not quite. It was a decisive victory for the Flemish community in which the commander of the French army, Robert II of Artois, was caught and killed on the battlefield. Moreover, the town militia slaughtered at least a thousand French cavaliers and collected thousands of golden spurs from their fallen foes that gave the battle its name.

Day of the Flemish Community, therefore, recalls the enormous victory against the French on July 11 every year by shutting down governmental offices, celebrating at the Grand Festival, and organizing cultural events.