The good relationship between the young William II (Count William IV of Hainault) and the bourgeois is Le Quesnoy resulted in the rapid construction of beautiful round towers surrounding the town (partially destroyed in the 16th Century on the construction of the new walls). In 1405 he reached his majority and was nicknamed "the Good". He was married first wife, Mary, daughter of the King of France, Charles V. His marriage was barren so he contracted a new alliance (12 April 1385) with Margaret, daughter of Philip the Bold, known for this reason, in the history of Le Quesnoy by the name of Margaret of Burgundy. Margaret stood out throughout her life by her good works, and moreover, she had to take an important role in the town. During his reign, William IV granted many privileges including to the bowmen of Le Quesnoy. Le Quesnoy reached its peak of power and fame. The town was well protected and supplied, and was able to sell to the towns of the Somme and others darts, crossbows and guns.