Epona is the Continental Celtic Horse Goddess who proved so popular She was adopted by the Romans. Shrines to Her could be found in stables, and it is likely the Romans brought Her worship with them to Britain, where She was unknown before, even though the people there were also of Celtic stock.
Her name comes from the Gaulish word for "horse", epos, which derives from the same root as both the Latin word for horse, equus and the Greek, hippos. Her name means "Divine Mare". Though Her name is said to give us our word "pony", the actual source of that word is from the Gaelic ponaidh and/or Irish poni.
Epona is shown here in the so-called Imperial pose,the usual depiction of Her outside of Gaul. She is seated between two of the little wild horses known in the Camargue, the marshy area in the south of France. These horses (by modern standards, ponies, since they average about 13 hands high) are descended from ones that escaped from the Romans when they were in the area. They are a strange-looking variety, with square heads and a fay look, and though they are born dark brown or black they become white when they are adults, though some of them keep the dark mane and tail.
Epona and Her friends are depicted within the head of the White Horse of Uffington, in Oxfordshire, England, with the Horse stretching out behind them and White Horse Vale in the background. The White Horse is likely a little too early to have been originally associated with Epona, as it's pre-Roman, and it was probably carved by a horse-worshipping Celtic tribe as a boundary marker.
Epona may well be related to the Welsh horse-goddess Rhiannon, for one of Epona's titles is "Queen"in the Latin, Regina, and in Gaulish, Rigatona, which later became the name Rhiannon.