“Epona was the Gaulish goddess of the horse, and the protector of horses and horsemen. She was, rather surprisingly, venerated by the Romans, being the only Gallo-Celtic deity to be adopted by them. The Roman cavalry in particular worshiped her, and shrines were erected in her honor in the major stables.
Epona was invariably depicted riding a mare, often accompanied by a foal or surrounded by a group of horses. ”
Excerpt from “The Horse, 30,000 Years of the Horse in Art” by Tamsin Pickeral.
I find it very interesting that the Romans adopted this deity. To me it indicates the Romans, who at that time ruled most of the known world, regarded horses as so important that it was critical to stay on the right side of any deities that governed the health and well being of horses and horsemen.