what is ashmedha

In aswamedha yagna, the sacrifical horse is allowed to roam around for a year. If the horse passed through a territory without facing any resistance from the ruler of that territory, then that territory would come under the control of the king performing the yagna. If the ruler of the territory refused to let the horse pass, then there would be a battle between that ruler and the king performing the yagna for control of the territory. After a year, the horse would be brought back and sacrificed as an offering to Agni, the god of fire.