History in this part of France is complicated but to try and explain the Flemish architecture and many of the names here is a (no-longer quite so) quick potted guide.
One method of acquiring territory (a synonym for power) was to marry well. As the formative centuries of France passed by it happened that many of the King’s vassals became more powerful than the king himself (e.g. William the Bastard of Normandy sails off in 1066 and becomes William the Conqueror, King of England).
One such family was that of Burgundy. The moment you hear the word you think; south of France and wine. But that is the area; in this case we are talking about the Dukes who were of royal lineage and came to own not only what we consider to be the wine region but also pretty much everything to the north of Paris, eastern France, Belgium and areas of Germany (to use current geopolitical terms).
France ran on a feudal system. The king was the tip of the pyramid but only actually owned the royal domain, he governed everything else through his vassals (The princes, dukes and so forth). Thus William (now Conqueror) may have been King of England in his own right but he was still a vassal of the French king by being the Duke of Normandy.
In fact then, for much of its history the French kings only owned a minority percentage of the territory and were vulnerable to houses such as Normandy and Burgundy.
When the French confiscated the Norman/English territories in France the powder was ignited and the Hundred Years War began.
Following the death in suspicious circumstances of its Duke, Burgundy sided with the English in 1419 against France. In fact Jeanne d’Arc was captured by the Duke’s men brought to Arras and eventually sold to the English.
The Treaty of Arras in 1435 brought a reconciliation between the two French parties and hastened the end of England’s chance of winning the war.
In 1461 Louis XI came to the French throne with an agenda of reunification on his mind (in other words: everything would be owned by the crown). It was almost inevitable that war would eventually break out between him and the last of the Dukes of Burgundy — Charles the Bold (Charles le Téméraire).
In 1477 the Duke met his demise at Nancy whilst fighting the French and Swiss but in an astute move Charles’ widow married their daughter off within months to Maximilian, the son of Frederick III the Holy Roman Emperor.
The marriage had far reaching effects because when Louis attempted to seize back what he considered to be a treacherous vassal’s possessions, Maximilian, a future emperor, intended to maintain what he now considered to be his.
It came down to treaties. In 1482 the first was signed in Arras. This returned Picardie and the Duchy of Burgundy to Louis. It was also agreed that the Dauphin Charles would marry Maximilian’s daughter Marguerite, bringing with her a dowry which included Artois. The second was signed at Senlis in 1493 after Charles decided that he wanted to marry somebody else. Marguerite was sent packing, and as France was in de facto possession of much of the old Burgundian territory she was lucky to be able to conserve Artois.