The ancient Celtic festival traditionally associated with May Day is Beltane. It is a Gaelic festival marking the beginning of summer and was historically observed especially in Ireland, Scotland, and the Isle of Man.
Beltane was one of four major Gaelic seasonal festivals. The others were Imbolc on February 1, Lughnasadh on August 1, and Samhain on November 1. Beltane was connected with moving cattle to summer pastures, so rituals often sought protection for livestock, crops, people, and dairy products.
Fire was central to the festival. Historical accounts describe bonfires whose flames, smoke, and ashes were believed to have protective powers. People and cattle could be led between fires, while household fires were sometimes extinguished and relit from the communal Beltane fire.
Beltane is not simply another name for every May Day celebration. It is the specifically Gaelic festival within a wider family of European May traditions. Modern Celtic cultural events and neopagan communities have revived many Beltane customs.