Between Guard changes, every half hour during the summer and one hour during the winter, a walk occurs. During the walk, soldiers take exactly 21 paces to both ends of a black mat. The Sentinels then pause for 21 seconds facing the Tomb. The 21 seconds is symbolic of the 21-gun salute, which is the highest military honor given.
Tomb of the
Unknowns
The Tomb of the Unknowns stands atop a hill overlooking Washington, D.C. The Tomb sarcophagus was placed above the grave of the Unknown Soldier of WWI. West of the WWI Unknown are the crypts of unknowns from WWII, Korea and Vietnam. Those three graves are marked with white marble slabs flush with the plaza.