In The Return of the King novel, Aragorn finds a route that goes through territory held by those Tolkien calls “the Dead.” They are supposedly spirit beings of people who died. And, Aragorn is faced with confronting them.
What is Necromancy?
“ When thou art come into the land which the Lord thy God giveth thee, thou shalt not learn to do after the abominations of those nations.  There shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch.  Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer.  For all that do these things are an abomination unto the Lord: and because of these abominations the Lord thy God doth drive them out from before thee.  Thou shalt be perfect with the Lord thy God.”
The belief that the spirits of dead people hang around the earth is a pagan and occult idea. The Bible says: