was a lustration or purification of the Roman people, by one of the censors in the Campus Martius, after the census, which was taken every five years, had been completed. This custom was first instituted by King Servius Tullius n.c. 566, and was afterwards kept up with great regularity at the periods just specified. In the earliest period of the Roman republic the census was taken, and the lustrum solemnized, not by the censors, as was afterwards the custom, but by the consuls. We gather from Livy (iii. 22, xxiv. 43), that the census sometimes took place without the lustrum being performed, owing probably to some great calamity which had happened to the republic. For the determination of the time when the lustrum took place, see Niebuhr, Hist. of Rome, i. p. 277.