This photo shows the procession through town with the reliquary which houses the holy candle of arras. The story behind the candle goes like this: Normand and Ithier are musicians. Normand kills the brother of Ithier. Obviously this puts some bad blood between them until angels and the virgin mary appear to them to tell them to make up. They do so, and the virgin gives them a candle, which they melt into water and give the water to sick people (probably plague victims), which makes them well.
According to the catholic encyclopedia, the candle is "said to have been given to Bishop Lambert in 1105 by the Blessed Virgin, to stop an epidemic." The names and story had changed by the 18th century, in a poem by the abbot H.-J. Du Laurens. It seems 'Jérôme' makes some comment about the fidelity of 'Jean's' wife. Later he gets castrated by some dogs, and repents (I'm not making this up!). There's an epidemic, the candle heals them. Next thing you know the candle is stolen, but retrieved, so they have a procession. It's crazy stuff - much more exciting than the 16th century version.