Totemistic taboo is also a possible reason for refusal to eat horse meat as an everyday food, but did not necessarily preclude ritual slaughter and consumption. Roman sources state that the goddess Epona was widely worshipped in Gaul and southern Britain. Epona, a triple-aspect goddess, was the protectress of the horse and horse keepers, and horses were sacrificed to her; she was paralleled by the Irish Macha and Welsh Rhiannon. In The White Goddess, Robert Graves argued that the taboo among Britons and their descendants was due to worship of Epona, and even earlier rites. The Uffington White Horse is probable evidence of ancient horse worship. The ancient Indian Kshatriyas engaged in horse sacrifice (Ashwamedh Yaghya) as recorded in the Vedas and Ramayana, but in the context of the ritual sacrifice, it is not 'killed', but instead smothered to death. In 1913, the Finnic Mari people of the Volga region were observed to practice a horse sacrifice.