For many Americans, Memorial Day signifies the start of the summer season, as well as a much-needed long weekend. But hanging out by the pool and roasting weenies wasn’t the original purpose of the day.

Memorial Day has been celebrated as a national holiday in the U.S. on the last Monday in May since the early 1970s. But its roots reach back a century before that, in the bloody past of the nation’s most divided time: the Civil War. In fact, some critics have complained that the holiday has drifted too far toward frivolous fun, and should be restored to a more respectful observance.

Memorial Day differs from Veterans Day, on November 11, which aims to celebrate and recognize all people who have served in the nation’s military branches. Memorial Day commemorates those who have lost their lives serving their country.

The day has long been marked by solemn parades and ceremonies and the placing of flowers on the graves of fallen service members, as well as lighter activities like sporting events.

Regardless of how it’s celebrated, the history of Memorial Day remains debated—and even controversial.

The U.S. Civil War was devastating for families on both sides of the conflict—nearly 500,000 men died, or about two percent of the U.S. population at the time. During the battle of Gettysburg, the Union and Confederacy lost more than 7,000.

In the years following the conflict, women, especially in the South, began tending to the graves of fallen soldiers, often regardless of which side they fought for. Their willingness to overlook past divisions was lauded in newspapers in the North. Their kindness was viewed as an olive branch to many, including northerner Francis Miles Finch, who wrote the popular poem “The Blue and The Grey” praising those efforts.