But on one day in the year a ram was killed, and its skin was placed on the statue of the god Ammon.(231) Now, if we knew the ritual of the Arician grove better, we might find the rule of excluding horses from it, like the rule of excluding goats from the Acropolis at Athens, was subject to an annual exception, a horse being once a year taken into the grove and sacrificed as an embodiment of the god Virbius. By the usual misunderstanding the horse thus killed would come in time to be regarded as an enemy offered up in sacrifice to the god whom he had injured, like the pig which was sacrificed to Demeter and Osiris or the goat which was sacrificed to Athene and Dionysus. It is so easy for a writer to record a rule without noticing an exception that we need not wonder at finding the rule of the Arician grove recorded without any mention of an exception such as I suppose. If we had had only the statements of Athenaeus and Pliny, we should have known only the rule which forbade the sacrifice of goats to Athene and excluded them from the Acropolis, without being aware of the important exception which the fortunate preservation of Varro’s work has revealed to us. The conjecture that once a year a horse may have been sacrificed in the Arician grove as a representative of the deity of the grove derives some support from the fact that a horse sacrifice of a similar character took place once a year at Rome. On the 15th of October in each year a chariot-race took place on the Field of Mars. The right-hand horse of the victorious team was sacrificed to Mars by being stabbed with a spear. The object of the sacrifice was to ensure good crops. The animal’s head was cut off and adorned with a string of loaves. The inhabitants of two wards—the Sacred Way and the Subura—then contended with each other who should get the head. If the people of the Sacred Way got it, they fastened it to a wall of the king’s house; if the people of the Subura got it, they fastened it to the Mamilian tower. The horse’s tail was cut off and carried to the king’s house with such speed that the blood dripped on the hearth of the house.(232) Further, it appears that the blood of the horse was caught and preserved till the 21st of April, when it was mixed by the Vestal virgins with the blood of the unborn calves which had been sacrificed six days before. The mixture was then distributed to shepherds, and used by them for fumigating their flocks.(233)