The Poplifugia is a lesser-known festival that was of obscure origin even for the Romans themselves; Macrobius says that it marked a Roman retreat from the Etruscans at Fidenae during the Gallic invasion, and that the Vitulatio commemorated their comeback victory.
It was a dies religiosus, a day of religious prohibition when people were to refrain from undertaking any activity other than attending to basic necessities.
The verb vitulari meant to chant or recite a formula with a joyful intonation and rhythm.
[4] Macrobius says vitulari is the equivalent of Greek paianizein (παιανίζειν), "to sing a paean," a song expressing triumph or thanksgiving.
One modern explanation relates the word Vitulatio to vitulus, "heifer," the animal that served as a ritual scapegoat at Iguvium, as described by the Iguvine Tablets.