Service members gathered Friday, for the annual ceremony to place flags on each of the gravestones at Arlington National Cemetery.

Soldiers from the 3rd U.S. Infantry, known as "The Old Guard," put each flag perfectly in place, exactly one foot from the marker.

It takes about three hours to place the flags in front of more than 260,000 gravestones and about 7,300 niches for soldiers who were cremated.

The Old Guard will stand watch over the flags through the Memorial Day weekend.

The ceremony -- known as "Flags In" -- has taken place each year for the past 40 years.