The (horse sacrifice) ashva medha was one of the most important and elaborate royal rituals in ancient India. The exact requirements for its performance are detailed in the 13th chapter of the SHATAPATHA BRAHMANA. The sacrifice could be performed for various purposes, but it was usually a means to demonstrate the king’s power.
The chosen horse would be left to run loose for one year. The horse would be followed by a large contingent of the king’s army, which would be charged to subdue whatever land the horse entered. At the end of the year, the horse would be sacrificed at a large festival.
The BRIHADARARANYAKA UPANISHAD within the Shatapatha Brahmana begins with a meditation upon the sacrificed horse as the universal reality and dwells upon the esoteric interpretation of this sacrifice. This sacrifice was performed by many kings throughout Indian history, probably for the last time in the 18th century.
Further reading: Julius Eggeling, trans. The Satapatha Brahmana, According to the Text of the Madhyamdina School (Delhi: Motilal Banarsidass, 1972); Steven Fuchs, The Vedic Horse Sacrifice in Its Cultural-Historical Rela-tions (New Delhi: Inter-India, 1996); J. C. Heesterman, The Inner Conflict of Tradition: Essays in Indian Ritual Kingship and Society (Chicago: University of Chicago Press, 1985.); Wendy Doniger O’Flaherty, Sexual Meta-phors and Animal Symbols in Indian Mythology (Delhi: Motilal Banarsidass, 1981).
Encyclopedia of Hinduism. A. Jones and James D. Ryan. 2007.