The origins of the Franco-Flemish War (1297–1305) can be traced back to the accession of Philip IV "the Fair" to the French throne in 1285. Philip hoped to reassert control over the County of Flanders, a semi-independent polity notionally part of the Kingdom of France, and possibly even to annex it into the crown lands of France. In the 1290s, Philip attempted to gain support from the Flemish aristocracy and succeeded in winning the allegiance of some local notables, including John of Avesnes (Count of Hainaut, Holland and Zeeland). He was opposed by a faction led by the Flemish knight Guy of Dampierre who attempted to form a marriage alliance with the English against Philip. In Flanders, however, many of the cities were split into factions known as the "Lilies" (Leliaerts), who were pro-French, and the "Claws" (Clauwaerts), led by Pieter de Coninck in Bruges, who advocated independence.
In June 1297, the French invaded Flanders and gained some rapid successes. The English, under Edward I, withdrew to face a war with Scotland and the Flemish and French signed a temporary armistice in 1297, the Truce of Sint-Baafs-Vijve, which halted the conflict. In January 1300, when the truce expired, the French invaded Flanders again and by May were in total control of the county. Guy of Dampierre was imprisoned and Philip himself toured Flanders making administrative changes.
After Philip left Flanders, unrest broke out again in the Flemish city of Bruges directed against the French governor of Flanders, Jacques de Châtillon. On 18 May 1302, rebellious citizens who had fled Bruges returned to the city and murdered every Frenchman they could find, an act known as the Bruges Matins. With Guy of Dampierre still imprisoned, command of the rebellion was taken by John and Guy of Namur. Most of the towns of the County of Flanders agreed to join the Bruges rebellion except for the city of Ghent which refused to take part. Most of the Flemish nobility also took the French side, fearful of what had become an attempt to take power by the lower classes.
In order to quell the revolt, Philip sent a powerful force led by Count Robert II of Artois to march on Bruges. Against the French, the Flemish under William of Jülich fielded a largely infantry force which was drawn mainly from Bruges, West Flanders and the east of the county. The city of Ypres sent a contingent of five hundred men under Jan van Renesse, and despite their city's refusal to join the revolt, Jan Borluut arrived with seven hundred volunteers from Ghent.
Fragments of original goedendags
preserved at the Kortrijk museum
The Flemish were primarily town militia who were well equipped and trained. The militia fought primarily as infantry, were organized by guild, and were equipped with steel helmets, mail haubergeons, spears, pikes, bows, crossbows and the goedendag. All Flemish troops at the battle had helmets, neck protection, iron or steel gloves and effective weapons, though not all could afford mail armor. The goedendag was a specifically Flemish weapon, made from a thick 5 feet (1.5 m)-long wooden shaft and topped with a steel spike. They were a well-organized force of 8,000–10,000 infantry, as well as four hundred noblemen, and the urban militias of the time prided themselves on their regular training and preparation. About 900 of the Flemish were crossbowmen. The Flemish militia formed a line formation against cavalry with goedendags and pikes pointed outward. Because of the high rate of defections among the Flemish nobility, there were few mounted knights on the Flemish side. The Annals of Ghent claimed that there were just ten cavalrymen in the Flemish force.
The French, by contrast, fielded a royal army with a core of 2,500 noble cavalry, including knights and squires, arrayed into ten formations of 250 armored horsemen. During the deployment for the battle, they were arranged into three battles, of which the first were to attack and the third to function as a rearguard and reserve. They were supported by about 5,500 infantry, a mix of crossbowmen, spearmen, and light infantry. The French had about 1,000 crossbowmen, most of whom were from the Kingdom of France and perhaps a few hundred were recruited from northern Italy and Spain. Contemporary military theory valued each knight as equal to roughly ten footmen.