@spendius,
OK I have a some what understanding, Maybe you would like to complete it?
Walpurgis has its roots in ancient pagan customs, superstitions and festivals. At this time of year, the Vikings participated in a ritual that they hoped would hasten the arrival of Spring weather and ensure fertility for their crops and livestock. They would light huge bonfires in hopes of scaring away evil spirits.
But the name "Walpurgis" comes from a very different source. In the 8th Century, a woman named Valborg (other iterations of the name include Walpurgis, Wealdburg and Valderburger) founded the Catholic convent of Heidenheim in Wurtemburg, Germany. She herself later became a nun and was known for speaking out against witchcraft and sorcery. She was canonized a saint on May 1, 779. Since the celebration of her sainthood and the old Viking festival occurred around the same time, over the years the festivals and traditions intermingled until the hybrid pagan-Catholic celebration became known as Valborgsmässoafton or Walpurgisnacht - Walpurgis Night.