What festival marks the beginning of summer in Celtic tradition? Beltane does. Also called Bealtaine or Bealltainn, it is a Gaelic seasonal festival traditionally celebrated on 1 May, midway between the spring equinox and summer solstice.
Beltane was one of four major Gaelic festivals, alongside Imbolc, Lughnasadh, and Samhain. Historically, it marked the start of the pastoral summer season, when cattle were moved to higher summer pastures. Communities used protective rituals to guard livestock, crops, people, and dairy products from disease or supernatural harm.
Bonfires were central to many recorded customs. Cattle were driven between fires, and household fires were sometimes extinguished and relit from the festival flame. People also decorated homes and animals with yellow May flowers and visited holy wells. Food and drink could be offered to the aos sí, the supernatural beings associated with the Otherworld.
A common mix-up is confusing Beltane with Samhain: Beltane begins summer, while Samhain traditionally begins winter. Modern neopagan celebrations draw on these older customs but are not identical reconstructions of ancient practice.