Ashvamedha
The Ashvamedha (Sanskrit: अश्वमेध aśvamedhá) is a horse sacrifice ritual followed by the Śrauta tradition of Vedic religion. It was used by ancient Indian kings to prove their imperial sovereignty: a horse accompanied by the king's warriors would be released to wander for a period of one year. In the territory traversed by the horse, any rival could dispute the king's authority by challenging the warriors accompanying it. After one year, if no enemy had managed to kill or capture the horse, the animal would be guided back to the king's capital. It would be then sacrificed in an elaborate Agnicayana ritual, and the king would be declared as an undisputed sovereign.
Broad outline
A stallion is selected and released for a year of wandering in the company of a hundred or more warriors. The king remains at home and turns over rulership to the adhvaryu who makes daily ghee libations into a footprint of the absent horse. The hotr recites evening narrations of the exploits of past kings. The release of the horse is considered an invitation to dispute the authority of the king. If the horse wanders into a territory controlled by someone who doesn't recognize the authority of the king, the rivals challenge the invading warriors accompanying the horse. After almost a year the horse is guided home, if no defending army has managed to kill or capture it.