Calan Mai

Calan Mai ([ˈkalan ˈmaɪ̯] "Calend (first day) of May") or Calan Haf ([ˈkalan ˈhaːv] "Calend of Summer") is a May Day holiday of Wales held on 1 May. Celebrations start on the evening before, known as May Eve, with bonfires; as with Calan Gaeaf or November 1, the night before (Welsh: Nos Galan Haf) is considered an Ysbrydnos or "spirit night" when spirits are out and about divination is possible. The tradition of lighting bonfires celebrating this occasion happened annually in South Wales until the middle of the 19th century.

Calan Haf parallels Beltane and other May Day traditions in Europe.

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Wikipedia