Epona is a Gaulish horse goddess, the protector of horses, mares, foals, donkeys and mules, and of the people who worked with them, and she holds a unique distinction among Celtic deities: she is the only one to have been taken fully into the official religion of Rome, given a place in the Roman calendar with a feast day of her own, on the eighteenth of December. Her name derives from the Gaulish word for horse, and she is regularly depicted seated among horses or foals, or riding side-saddle on a mare, often holding a dish of grain, fruit or a cornucopia, signs of the fertility and abundance she was also thought to bring. Her cult, originating among the horse-rearing Celts of Gaul, spread widely through the Roman world, carried above all by the cavalry: Roman mounted troops, and especially the auxiliary units recruited from Gaul and the Germanies, adopted her as their patroness, and she was honoured in the stables of the army from Britain to the Danube, sometimes with a small shrine set up where the horses were kept.
Because of this military following, dedications and images of Epona are found across a great swathe of the empire, making her one of the best-attested of all Celtic deities. She protected the animals on which agriculture, transport and war all depended, and through her association with horses she was drawn also toward ideas of fertility, sovereignty and, in some interpretations, the passage to the otherworld. Epona is a striking case of a native Celtic goddess who not only survived the Roman conquest but was embraced by the conquerors and carried by their armies to the far corners of their world.