Lustration, in ancient Rome, a ceremony of solemn purification or consecration of the Roman people, by means of an expiatory sacrifice, which was performed after every census. The sacrifice consisted of a bull, a sow and a sheep or ram. The ram was dedicated to Jupiter, the swine to Ceres and the bull to Mars. As this lustration took place at the end of every five years,
lustrum came to signify a period of five years.