A Sentinel from the 3rd U.S. Infantry Regiment performs ceremonial duties during a Changing of the Guard demonstration at the Arlington National Cemetery’s Tomb of the Unknown Soldier in Arlington, Va., Oct. 22, 2021. This year marks the 100th anniversary of The Tomb of the Unknown Soldier – a lasting symbol of the courage, bravery, and sacrifices of generations of American Soldiers. The nation is forever indebted to all who have served our nation and made the ultimate sacrifice for freedom. (U.S. Army photo by Greg Nash)