Equus October: The October Horse
Two-horse chariot races were held on the Ides of October in honor of Mars. The inner horse of the winning team became the "October Horse." Upon the Campus Martius he was sacrificed by thrusting the sacred spear of Mars into his heart. His blood was collected and it is believed that it was mixed by the Vestales Virgines with the ashes of the unborn calf that was sacrificed at the Fordicidia in April and distributed as februa to the people for Parilia (21 April). His tail was cut off with a morsel of flesh as an offa penita and rushed to the Regia where the blood was allowed to drip slowly into the sacred hearth. The horse's head was cut off and decked with cakes and ribbons in the same manner as draught animals at Vestalia, Consualia, and the feriae Sementivae. Paulus mentions that these cakes came from the recent harvest. The decorated horse head then became a trophy contested over by men from the neighborhoods of the Via Sacra and the Subura. If the team from the Via Sacra were able to carry off the horse, then his head was affixed to the Regia. If instead the men from Subura carry it away, the head was affixed on the turris Mamilia as a fetish to ensure fertility and virility in the coming year.
Fasti Philocalus; Festus 178; Paulus 220; Plutarch Ques. Rom. 97; Polybius 12.4. Ovid, Fasti; Fowler, W. W. (1899) The Roman Festivals of the Period of the Roman Republic, London.