The Roman festival that commemorated the dead and was observed in May was Lemuria.
Lemuria, also called Lemuralia, was held on May 9, 11, and 13 in the Julian calendar. Romans believed that restless or malevolent spirits, called lemures or larvae, could trouble the household. The festival’s purpose was to drive these ghosts away and restore domestic peace.
According to the poet Ovid, the head of the household performed the central rite at midnight. Walking barefoot, he washed his hands, cast black beans behind him as offerings, and repeated a formula nine times. Other family members struck bronze vessels and called on the ancestral spirits to leave. The ritual reflects Roman anxiety about people who had died violently, prematurely, or without proper funeral rites.
Lemuria is often confused with Parentalia, a February observance honoring deceased ancestors, or Feralia, the closing day of that festival period. Another later tradition associates May 13 with the Christian feast honoring martyrs and, eventually, the history of All Saints’ Day.