In ancient Roman tradition, the ceremony that formally named a newborn on the eighth or ninth day was called the dies lustricus.
The dies lustricus was a purification and naming ceremony in Roman family life. For girls it was traditionally held on the eighth day after birth, while for boys it was held on the ninth. The child received a bulla, an amulet worn for protection, and the family formally recognized the infant’s name.
The day was connected with ritual purification and the child’s incorporation into the household and wider social world. Roman naming practices also differed by sex and status, so the ceremony should not be reduced to a modern birth-registration event.
It is distinct from the ancient Greek amphidromia, which involved carrying a newborn around the household hearth. Both were early-life ceremonies, but they belonged to different cultures and had different ritual meanings.