Panibus redimibant caput equi immolati idibus Octobribus in campo Martio, quia id sacrificium fiebat ob frugum eventum; et equus potius quam bos immolabatur, quod hic bello, bos frugibus pariendis est aptus.

They used to crown the head of the horse sacrificed on the Ides of October in the Campus Martius with loaves of bread, because that sacrifice was made for the success of the crops; and a horse was sacrificed rather than a cow, because the horse is suited to war, while the cow is suited to bringing forth crops.