In ancient Rome, these were ghosts of people who died without a surviving family, or a ghost evil in nature. The lemures were one of two classes of ghosts in Roman belief and were associated with larvae or evil spirits.
The Romans considered it a curse to die without surviving issue. Thus, those who did so were doomed to become lemures. Other lemures included the spirits of those who had died prematurely and were trapped on the earth until their allotted lifespan was up; victims of murder and violent death; executed criminals; and drowning victims. To prevent a lemure from returning from the grave, the Romans burned black beans around the tomb as the body was interred. If a lemure succeeded in haunting the living, it was exorcised by banging on drums.
Lemures were propitiated each year at a festival called Lemuria.
--- Ghosts & Spirits by Rosemary Ellen Guiley, p. 217