The Tomb of the Unknown Soldier in Arlington National Cemetery marked its 100th anniversary this week.

On November 11, 1921, an unidentified U.S. infantryman who died in World War I was laid to rest there after a three day ceremony (watch footage from the U.S. National Archives above).

President Warren G. Harding placed the Medal of Honor, the nation’s highest military decoration, on the casket and Americans across the country observed two minutes of silence.

The Tomb’s sarcophagus was adorned with three figures that represent Peace, Victory and Valor. It features the inscription: “Here rests in honored glory an American soldier known but to God.”

Decades later, in 1958, two additional unknown soldiers from World War II and the Korean War were interred at the site. A fourth solider, from the Vietnam war, was added to the Tomb in 1984. He was later identified as 1st Lt. Michael Blassie and he was relocated to a family plot in Missouri.

For the past 96 years, visitors have been unable to approach the Tomb, which is protected by 3rd Infantry Regiment soldiers – dubbed  “The Old Guard” – around the clock. But on Tuesday and Wednesday, members of the public were allowed to lay flowers before the sacred memorial.

“As you lay your flower, we at Arlington encourage you to reflect on the meaning of the Tomb. By the simple act of laying a flower, you are not only honoring the three unknowns buried here but all unknown or missing American service members who made the ultimate sacrifice in service to our nation,” Tim Frank, the Arlington National Cemetery’s historian, said during Tuesday’s opening ceremony.

To commemorate Veteran’s Day, President Joe Biden offered remarks at the Tomb on Thursday and participated in a wreath laying ceremony.

“To be a veteran is to have endured and survived challenges most Americans will never know…and you’ve done it for us. You’ve done it for America,” he said.

“Our veterans represent the best of America,” he added. “You are the very spine of America. Not just the backbone, you’re the spine of this country. And all of us — all of us — owe you.”

“We have many obligations,” the president continued “but one truly sacred obligation: to properly prepare those and equip those who we send into harm’s way, and care for them and their families. This is a lifetime sacred commitment. It never expires.”

He urged veterans experiencing mental health issues to seek help. “If you’re struggling, reach out…If you’re having trouble, thinking about things, it’s no different than if you had a wound in your arm.”

Biden also made reference to his deceased son, Beau, who served in Iraq and was awarded the Bronze Star.

“For me and for Jill and for the entire Biden family, it’s personal” he said.