The Ides of October marked the end of the campaigning season, and on that day a race was held on the grassy sward of the Campus Martius, just outside the Servian Walls of Republican Rome.
The year's best war horses were harnessed in pairs to chariots and driven at breakneck pace; the right-hand one of the winning pair became the October Horse, and was ritually killed with a spear by the flamen Martialis,
the special priest of Mars, who was god of war. Then the October Horse's head and genitalia were amputated. The genitals were rushed to bleed on the sacred hearth in the Regia, Rome's oldest temple, after which...