Here rests in honored glory an American soldier known but to God.
A solitary Sentinel guard marches in front of the Tomb of the Unknowns at Arlington National Cemetery near Washington, D.C.
A sacred ritual
The Tomb of the Unknowns is dedicated to American service members who have died without their remains being identified.
It is considered one of the highest honors to be a Sentinel at the Tomb of the Unknowns. Those who perform this sacred ritual are elite members of the 3rd U. S. Infantry Regiment.
With each rotation back and forth, a Sentinel guard marches exactly 21 measured steps, turns and faces east for 21 seconds, turns and faces north for 21 seconds, takes 21 steps down the mat and repeats the process.
Twenty-one steps refers to the 21-gun salute, the highest honor that can be bestowed on a service member. A 21-gun salute is usually reserved for presidents or former presidents, heads of state or reigning monarchs.
Tradition started after first World War
Congress first approved the burial of an unidentified American soldier in the plaza of the new Memorial Amphitheater in 1921.
That year on Armistice Day, November 11, President Warren G. Harding officiated at the interment of an American soldier who fought in World War I, whose remains were brought back from France. Other Unknowns have been interred there since.
24 hours a day, 365 days a year
Every hour at the sound of the clock tower bells, a uniformed relief commander appears on the plaza to announce the changing of the guard.
Spectators are asked to stand and remain silent. Then the relief commander and the relieving Sentinel meet the retiring Sentinel in the middle of the matted path to salute the Unknown.
With scrupulous care, this solemn rotation of the Sentinel guards has gone on 24 hours a day, 365 days a year since 1937.