Cenotaph

Webster's Dictionary

(n.) An empty tomb or a monument erected in honor of a person who is buried elsewhere.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature

an empty monument erected by the ancient Greeks and Romans in honor of the dead who were either buried elsewhere or whose bodies could not be found. After the structures were completed the souls of the dead, for whom they were intended, were thrice called upon by name to occupy the habitations prepared for them.