June 19 is an important day in history, known as Juneteenth. Yet many people may not actually know just what the day is, what it celebrates, or why it still matters.

For some people, Monday, June 19 is just another day, and another insignificant day on the calendar. However, for those who are direct descendants of former slaves, the day holds a much bigger significance, as it is the oldest known celebration to commemorate the ending of slavery in the United States.

Read: 7 Surprising Facts About The History Of Juneteenth

According to Juneteenth.com, June 19, 1865 was the date that Union soldiers, led by Major General Gordon Granger, landed at Galveston, Texas and brought the news that the Civil War was officially over and those who had previously been enslaved were not free men and women. The website notes how important that is in relation to President Abraham Lincoln’s famous Emancipation Proclamation, which had become official two and a half years earlier, on January 1, 1863.

“The Emancipation Proclamation had little impact on the Texans due to the minimal number of Union troops to enforce the new Executive Order,” the website states. “However, with the surrender of General Lee in April of 1865 and the arrival of General Granger’s regiment, the forces were finally strong enough to influence and overcome the resistance.”

It has never truly been discovered why it took so long for slavery to officially end in Texas after the President’s initial order, with several theories floated around—including ones where a messenger was murdered en route to deliver the news and slaveowners deliberately withheld the news in order to keep their labor force in tact on the plantations. However, none have been proven to be true or false.

Though slavery has been out of practice for over 150 years, Juneteenth is still a day that is celebrated among many who want to make sure the relevance of the day isn't forgotten. Several events will take place around the United States to commemorate the special day.

Read: 10 Quotes About Slavery And Freedom In Honor Of Juneteenth

Among events taking place on Monday are:

The Dallas Juneteenth Festival: 2-7 p.m. at the Martin Luther King Jr. Community Center: Hosted by both the City of Dallas and Miles of Freedom, this free festival includes local vendors, live entertainment, food, arts and crafts, games, bounce houses, a petting zoo, free giveaways and more.

Most events commemorating the day were actually celebrated the weekend prior however. Events kicked off as early as Thursday in Pittsburgh, as well as in Rock Hill, South Carolina. Friday saw the annual Juneteenth Parade and Music Festival in Atlanta, two different community center events in Seattle, and a gospel concert in Chandler, Arizona. Celebrations continued on Saturday with both the Juneteenth International Celebration and KBAC festivals in Seattle, as well as four different events in Tempe, Tucson, Phoenix and Yuma Arizona. Syracuse, New York, also celebrated over the weekend with an annual festival on Sunday.