Ambrose Bierce
Monument, n. A structure intended to commemorate something which either needs no commemoration or cannot be commemorated.
The bones of Agememnon [sic] are a show
And ruined is his royal monument.
but Agamemnon's fame suffers no diminution in consequence. The monument custom has its reductiones ad absurdum in monuments "to the unknown dead"—that is to say, monuments to perpetuate the memory of those who have left no memory.
(Ambrose Bierce, The Devil's Dictionary, c. 1911)