The EQUIRRIA or October equus: Roman Festivals – sacrifice of a horse to Mars. The Equirria (Festival of Mars – held on February 27, First Equirria and March 14, Second Equirria) were holy days with religious and military significance at either end of the new year celebrations for Mars. The Roman state placed great emphasis on celebrating the god of war – to support the army, and to boost public morale. Priests performed rites purifying of the army. Celebrants held horse races on the Campius Martius (field of Mars), and drove a scapegoat (literally, a goat) out of the city of Rome, expelling the old and bringing in the new.

Equus October was a festival on October 15 (idus), in which the right hand horse of the winning pair of a race was sacrificed to Mars. The tail was rushed to the regia to have its blood drip on the hearth there. There was a traditional fight over its head between the inhabitants of the Subura who wanted it for the Turris Mamilia, and those of the Via Sacria who wanted it for the regia.