It happened during the 1574
second siege of Leiden, during the Dutch war of independence. The town was at wit's end and would have surrendered but for the brutality of the Spanish-led Habsburg army, which routinely executed practically all of the military plus a part of the civilian population of a town that surrendered. Leiden was finally relieved because the rebels succeeded in breaking the dikes, flooding the surrounding land. As a reward (but mainly because first choice Dordrecht was occupied by Habsburg troops), Leiden received the country's first university.
If you look at Leiden with Google earth or Google maps, you can clearly see where the city walls once stood, because the surrounding star-shaped moats still exist. The (now built-up) area called Lammeschans (to the Southeast on the road to the A12 motorway and on to Stompwijk en Zoetermeer) is where the Spanish headquarters were.
While the rebels were largely protestants, the Habsburg army was catholic and religion was one of the main issues of the revolt. What lead to using bibles was the consacration of the town's main churches for the protestant religion. The result was that the town suddenly had a large surplus of catholic bibles on its hands.
Leiden went on to become the first industrialized area in the world, the birthplace of Rembrandt and the meeting point for the pilgrim fathers (house is marked with a brass plaque). There were so many windmills in and around the city that people complained. Industry workers (mainly spinners, weavers and textile traders) were a rowdy, hard-drinking lot living off starvation wages and making impossibly long hours, but there was work for all comers and some got wealthy. Among my ancestors were two brothers from the lands of the bishop of Liege, who went to Leiden, got married to a local girl in a protestant church and joined the proletariat. One of the latest additions to the family tree, my daughter, studied in Leiden. One of the auditoriums she went to was once the main hall of the 5 centuries old prison. Doors can still be opened on one side only and windows are heavily barred...
At the date of the relief, 3rd October, Leiden throws a great party for itself. In summer, amateur actors recreate Rembrandt's "night watch" in 3 dimensions. All great fun.
Peter