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 similar sacrifice of a horse which took place once a year at Rome. On the fifteenth of October in each year a chariot-race was run on the Field of Mars. Stabbed with a spear, the right-hand horse of the victorious team was then sacrificed to Mars for the purpose of ensuring good crops, and its head was cut off and adorned with a string of loaves. Thereupon the inhabitants of two wardsthe Sacred Way and the Suburacontended 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. Further, it appears that the blood of the horse was caught and preserved till the twenty-first of April, when the Vestal Virgins mixed it 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.
In this ceremony the decoration of the horse's head with a string of loaves, and the alleged object of the sacrifice, namely, to procure a good harvest, seem to indicate that the horse was killed as one of those animal representatives of the corn-spirit of which we have found so many examples.
The custom of cutting off the horse's tail is like the African custom of cutting off the tails of the oxen and sacrificing them to obtain a good crop.
In both the Roman and the African custom the animal apparently stands for the corn-spirit, and its fructifying power is supposed to reside especially in its tail. The latter idea occurs, as we have seen, in European folk-lore. Again, the practice of fumigating the cattle in spring with the blood of the horse may be compared with the practice of giving the Old Wife, the Maiden, or the clyack sheaf as fodder to the horses in spring or the cattle at Christmas, and giving the Yule Boar to the ploughing oxen or horses to eat in spring. All these usages aim at ensuring the blessing of the corn-spirit on the homestead and its inmates and storing it up for another year.
The Roman sacrifice of the October horse, as it was called, carries us back to the early days when the Subura, afterwards a low and squalid quarter of the great metropolis, was still a separate village, whose inhabitants engaged in a friendly contest on the harvest-field with their neighbours of Rome, then a little rural town. The Field of Mars on which the ceremony took place lay beside the Tiber, and formed part of the king's domain down to the abolition of the monarchy. For tradition ran that at the time when the last of the kings was driven from Rome, the corn stood ripe for the sickle on the crown lands beside the river; but no one would eat the accursed grain and it was flung into the river in such heaps that, the water being low with the summer heat, it formed the nucleus of an island. The horse sacrifice was thus an old autumn custom observed upon the king's corn-fields at the end of the harvest. The tail and blood of the horse, as the chief parts of the corn-spirit's representative, were taken to the king's house and kept there; just as in Germany the harvest-cock is nailed on the gable or over the door of the farmhouse; and as the last sheaf, in the form of the Maiden, is carried home and kept over the fireplace in the Highlands of Scotland. Thus the blessing of the corn-spirit was brought to the king's house and hearth and, through them, to the community of which he was the head. Similarly in the spring and autumn customs of Northern Europe the May-pole is sometimes set up in front of the house of the mayor or burgomaster, and the last sheaf at harvest is brought to him as the head of the village. But while the tail and blood fell to the king, the neighbouring village of the Subura, which no doubt once had a similar ceremony of its own, was gratified by being allowed to compete for the prize of the horse's head. The Mamilian tower, to which the Suburans nailed the horse's head when they succeeded in carrying it off, appears to have been a peel-tower or keep of the old Mamilian family, the magnates of the village. The ceremony thus performed on the king's fields and at his house on behalf of the whole town and of the neighbouring village presupposes a time when each township performed a similar ceremony on its own fields. In the rural districts of Latium the villages may have continued to observe the custom, each on its own land, long after the Roman hamlets had merged their separate harvest-homes in the common celebration on the king's lands. There is no intrinsic improbability in the supposition that the sacred grove of Aricia, like the Field of Mars at Rome, may have been the scene of a common harvest celebration, at which a horse was sacrificed with the same rude rites on behalf of the neighbouring villages. The horse would represent the fructifying spirit both of the tree and of the corn, for the two ideas melt into each other, as we see in customs like the Harvest-May.