The ancient Celts and their Druids worshipped over 300 deities.  (Like Carrie Bradshaw and her shoes, they could never have too many.)  Epona is the Horse Goddess, from whom the word ‘pony’ is derived.  She became the only Celtic deity to be worshipped in Rome, and her feast day, Eponalia, is next Sunday, the 18th of December. 
Ancient peoples from the west of Ireland, to as far east as Anatolia (Turkey), from the Danube River to Yugoslavia, down to Rome and even North Africa, worshipped the Horse Goddess.  Her Facebook fan page would have broken world records. 
Recently, I read a book on Celtic Myth written by a woman who lives in Texas.  She wrote that the Irish version of the Goddess Epona was named ‘Mare’ and that she was the bringer of bad dreams (night-mares). 

I love the books written about Celtic Mythology by people who’ve only visited Ireland or Scotland or Wales once or twice in their lives.  They frequently says things like, ‘Up until the beginning of the 20th Century, Irish people used to [do some wacky thing or other], carrying out this age-old custom.’  Frequently, nobody – including historians who have lived in and researched this Celtic country all their lives – has ever heard or read of said ‘age-old custom’.  The Texas woman who wrote that book was probably the victim of some old geezer who enjoyed dousing her with a large bucket of blarney. 

There is no Irish Goddess named ‘Mare.’  But there is a very famous one named Macha and she was associated with war, HORSES, sovereignty, and the site of the prehistoric fort of Emain Macha (which was named after her), near present-day Armagh in Northern Ireland.   And, because one can never have too many, the Irish mythological figure of Ếtain, also associated with Emain Macha, was considered a horse goddess, in a later historical period. 
 Epona was worshiped in England as well, where Bronze Age people painstakingly created the Uffington Horse.  The horse goddess was also known as “Rigantona” or “Rig Antonia,” which means “Great Queen.”  Some historians believe that the legend of Lady Godiva is directly related to Epona and other ancient fertility rituals, such as the mating of the High King with the white mare (but that’s another post in itself).  In Wales, the goddess Rhiannon, whose worship occurred at a much later point in time, was strongly associated with Epona. 
Epona was known by a variety of other names, which changed according to the language and myth of each particular region.  But no matter what she was called, her image remained similar.  She appeared as a woman with very long hair who was riding sidesaddle upon a white mare, or as a long-haired woman, lying naked on a white mare. 

Celtic Druids had totem animals, much like Native Americans.  The horse, and the white horse in particular, was a powerful totem, symbolising the Goddess herself, the land and journeying (both physical and spiritual).  The horse goddess was associated with the life cycle of birth-death-afterlife-rebirth, and hence, sexuality and the fertility of humans and the earth itself.  In this way, the horse and the Horse Goddess, could help humans transcend the limitations of mortality. 

With all this in mind, I plan to go visit my neighbour horses (Connemara ponies) at the lakeside and offer them a bucketful of carrots and apples so we can celebrate this feast day in style. 

Best wishes for a safe and happy Eponalia to you and yours!