On Thursday, members of the 3rd U.S. Infantry Regiment, or The Old Guard placed American flags at the gravesites of service members buried at Arlington National Cemetery.

This tradition, known as “flags in” has been held for more than 60 years, with every available soldier in the regiment placing small American flags at each headstone before Memorial Day weekend to honor fallen service members.

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According to Arlington National Cemetery’s website, within four hours, they place flags at more than 228,000 headstones and at more than 7,000 niche rows in the Columbarium Courts and the Niche Wall.

Flags are also placed at the Tomb of the Union Soldier, and at the memorials on Chaplain’s Hill. Meanwhile, 14,000 flags are placed at the Soldiers’ and Airmen’s Home National Cemetery.

All flags are removed after Memorial Day, prior to the cemetery opening.

The Old Guard has been designated as a ceremonial unit since 1948.