WASHINGTON — Despite the 90-degree heat and humidity, more than 1,000 soldiers gathered to participate in a 68-year-old tradition Thursday at Arlington National Cemetery.

The 3rd U.S. Infantry Regiment, known as the Old Guard, spent four hours placing small American flags in front of more than 230,000 grave markers to honor fallen soldiers.

Staff Sergeant Sean Hackshaw, 27, said he was happy to participate in the event, called “Flags-In.”

“Flags-In is about the soldiers of the present honoring and paying homage to the soldiers from the past who laid the foundation and the framework for us to be here today and do our jobs,” Hackshaw said.

Soldiers center the flags one foot in front of each grave marker, according to a news release from the U.S. Army Military District of Washington.

Hackshaw said soldiers use their boots to measure the placement. Because boot size varies from soldier to soldier, he said one person is in charge of an entire row to ensure precise, uniform placement.

“If it’s not done correctly, [the soldier] will redo it until it’s done to standard,” he said.

The tradition began in 1948 when the Old Guard became the Army’s official ceremonial unit, the news release said. The event takes place every year before Memorial Day weekend.

Hackshaw said it is important to remember the real reason behind the long weekend Americans celebrate each year.

“While it’s always fun to have three or four days off after a hard week’s work, just really think about the soldiers […] who laid this frame for us today to be a country […] and to have the things that we have today,” he said.

Rachel Nania contributed to this story.