Soldiers are placing nearly a quarter of a million U.S. flags at Arlington National Cemetery as part of a Memorial Day tradition.

The event Thursday is known as "flags in." It marks the beginning of Memorial Day weekend activities at the cemetery.

The U.S. Army Military District of Washington says in a statement that the tradition began in 1948. The mission is carried out by the 3rd U.S. Infantry Regiment, nicknamed "The Old Guard." The unit puts every available soldier to work, planting small flags in front of the more than 230,000 grave markers.

The soldiers also place about 14,000 flags at the Soldiers' and Airmen's Home National Cemetery in Washington.

The flags are removed after Memorial Day, before the cemeteries open to the public.