Here rests in honored glory an American soldier known but to God

Twenty-one steps south. Face east 21 seconds. Face north 21 seconds. Twenty-one steps north. Face east 21 seconds. Face south 21 seconds. Repeat until relieved.

This is the meticulous routine performed by the select few chosen for the honor of guarding the Tomb of the Unknown Soldier, located in Arlington National Cemetery, just outside of Washington, D.C. These Tomb Guard Sentinels, elite volunteer members of the U.S. Army’s 3rd U.S. Infantry Regiment, watch the Tomb 24 hours a day, 365 days a year, rain or shine — and have done so for almost 80 years.

The Tomb of the Unknown Soldier was constructed in 1921, after Congress approved the burial of an unidentified U.S. soldier from World War I, with other Unknowns interred since. The Tomb has been guarded year-round continuously since 1937, when the first 24-hour guards were posted. Since April 1948, sentinels from the 3rd U.S. Infantry Regiment, also known as the “Old Guard,” have been watching over the hallowed memorial.

Sentinels pace back and forth in front of the Tomb, taking 21 steps north and south, and standing for periods of 21 seconds at either side — 21 symbolizing the military’s “highest honor” of the 21-gun salute. While on duty, the soldiers do not wear rank insignia, as to not outrank the Unknowns. The guards are relieved at the top of every hour, except during visitor hours in the summer months, when the guard is changed on the half hour. When relieved, an elaborate ritual known as the “Changing of the Guard” occurs, which Arlington National Cemetery’s website details:

An impeccably uniformed relief commander appears on the plaza to announce the Changing of the Guard. Soon the new sentinel leaves the Quarters and unlocks the bolt of his or her M-14 rifle to signal to the relief commander to start the ceremony. The relief commander walks out to the Tomb and salutes, then faces the spectators and asks them to stand and stay silent during the ceremony.

The relief commander conducts a detailed white-glove inspection of the weapon, checking each part of the rifle once. Then, the relief commander and the relieving sentinel meet the retiring sentinel at the center of the matted path in front of the Tomb. All three salute the Unknown who have been symbolically given the Medal of Honor. Then the relief commander orders the relieved sentinel, “Pass on your orders.” The current sentinel commands, “Post and orders, remain as directed.” The newly posted sentinel replies, “Orders acknowledged,” and steps into position on the black mat. When the relief commander passes by, the new sentinel begins walking at a cadence of 90 steps per minute.

The above video shows a complete changing of the guard ceremony edited together from three different ceremonies all recorded on May 20, 2015. To watch the video at full resolution, be sure to choose the 4K option in the YouTube player.

The video was shot and produced by Justin Scuiletti. Special thanks to Arlington National Cemetery and Sgt. 1st Class Nicolas Morales for helping in the production of this video.