Beltane is the Celtic festival that marks the beginning of summer and is associated with fairies. It is traditionally observed on 1 May, around the midpoint between the spring equinox and summer solstice.
Historically, Beltane marked the start of the pastoral summer season, when cattle were moved to summer grazing. Communities lit bonfires and used their flames, smoke, and ashes in protective rituals for people, animals, crops, and dairy products. In some traditions, cattle or people passed between or over the fires.
Beltane is one of the four major Gaelic seasonal festivals, alongside Imbolc, Lughnasadh, and Samhain. The aos sí—often described as fairies or supernatural spirits—were thought to be especially active at Beltane, so offerings and rituals aimed to preserve good relations with them. Samhain is the common mix-up: it begins the winter half of the year, not summer.