The Jefferson Memorial is a national monument.
national monument definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a natural geographical feature or historic site, as a mountain, canyon, old fort, etc., maintained and preserved by the federal government for the public to visit
national monument definition by American Heritage Dictionary
A natural landmark or a structure or site of historic interest set aside by a national government and maintained for public enjoyment or study.