Memorial Day is perhaps the most somber day on Americans' calendars.

Each year, we pause to remember the men and women who made the ultimate sacrifice in service to their country in wars both at home and abroad.

Here are a few interesting facts about Memorial Day, courtesy of the Library of Congress:

Memorial Day began as Decoration Day

In the years directly following the Civil War, Americans across the country were still mourning the deaths of the more than 600,000 men who died during four long years of war. In small towns across the country, both North and South, veterans would decorate their comrades' graves with flowers.

The holiday began as Decoration Day on May 5, 1868, three years after the end of the Civil War. John Logan, a veteran of the war and head of the Union veterans organization the Grand Army of the Republic, established Decoration Day to be recognized on May 30, according to the U.S. Department of Veterans Affairs.

On that date, people on both sides of the war would be encouraged to place flowers on the graves of their relatives, friends or comrades who fell in battle. He picked May 30 because flowers would be in full bloom during that time.

Decoration Day only recognized fallen soldiers of the Civil War until World War I

While America's participation in World War I sometimes takes a backseat to the Revolutionary War, Civil War, World War II and the Vietnam War, it nevertheless helped establish many American traditions, including Veterans Day on Nov. 11, originally called Armistice Day.

World War I also changed how Decoration Day was celebrated in the U.S. The war was America's major first conflict since the Civil War, and the first major war fought exclusively on foreign soil.

The tradition of Decoration Day soon evolved from remembering just the fallen of the Civil War to remembering all soldiers who died during the country's wars at home and abroad

Memorial Day was not an official holiday until 1968

By the 1960s, Decoration Day had given way to Memorial Day. While there were several Memorial Day events and ceremonies across the country, it still was not recognized as a federal holiday. That changed with the passing of the Uniform Monday Holiday Act.

The act established several American holidays to fall on certain Mondays throughout the year, including Washington's Birthday (unofficially called Presidents Day) in February, Memorial Day in May, Labor Day in September, Columbus Day in October and Veterans Day in November, though the latter was later moved back to its original date of Nov. 11.

Memorial Day is one of the few days flags are ordered to fly at half-staff then full-staff.

While Memorial Day has spawned many traditions within communities, it also spawned several traditions by how the government observes the day as well.

Memorial Day has its own unique flag etiquette. At sunrise, anyone flying a flag should raise the flag briskly to full-staff then slowly lower the flag to half-staff. This is to honor the men and women who have fallen in the line of duty. At noon, the flag should be briskly raised to full-staff. This is to salute all of those who have served.

So even though Memorial Day Weekend is labeled as the “unofficial start of summer” and is filled with the openings of pools, barbecues and sales at retailers, let’s not lose sight of the real purpose behind the holiday.

— JGG