On-line friend Direcleit kindly pointed me to an article in the Book of Hallowe'en, available to view free on the Internet. It refers to the background to Walpurgis Night, which I mentioned a few days ago. I would recommend other texts in that book as well, which mainly focuses on Hallowe'en.
Walpurgis Night is the counterpoint to Hallowe'en, being the time when the wintertime is said to end, as opposed to Hallowe'en which is the day that summer ends. I close with an image of the Walburgskerk [Walpurgis Church] in the town of Zutphen, 70 miles east of Amsterdam in Holland. Another church of the same name stands 20 miles to the south, in Arnhem.