For 60 years, the annual Remembrance Day parade has attracted thousands of people to Gettysburg, Pennsylvania for festivities to honor the sweeping words Abraham Lincoln offered at the dedication of the Soldiers' National Cemetery.

The four-minute speech became known as the Gettysburg Address.

The parade attracts many descendants of the Union and Confederate soldiers who fought at Gettysburg from around the country who are also there to pay respect to their forebears at the surrounding battlegrounds.

This year marks the first time a warning has been directed at the parade through a letter sent to the Gettysburg Times—which the local newspaper forwarded to the authorities, resulting in the FBI calling it a "credible threat."

The weekend event organizer, Sons of Veterans of the Civil War, a fraternal organization dedicated to preserving the history those who fought and worked to save the Union, posted on the organization website, “I want to ensure you that the Sons Veterans Reserve Leadership is working in close cooperation with the Gettysburg Police, the National Park Police, and many other law enforcement agencies to ensure that we have a safe and successful weekend.”

Local authorities said they are investigating the threat made against the annual event set for Saturday as well as increasing security and working with the state police and the FBI to keep attendees secure throughout the weekend.

The local Fox 43 affiliate in Harrisburg reported Thursday it was not the first threat made towards an event in Gettysburg, “Police citing recent demonstrations by the activist group Antifa. However, they say it is the most serious, urging people to stay vigilant.”

The Gettysburg Borough Police Department and the Mayor advised people attending the event to not bring backpacks or coolers to the parade route or other scheduled events and to report any suspicious activity to police.

The Gettysburg Remembrance Day Parade Facebook page warned visitors to not bring caps, powder, or ammunition this weekend.

They also warned in that same post to not engage with "anti-Confederate groups" that might be in town over the weekend:

If and we say if any of the so called "anti-Confederate groups" are in the crowds PLEASE DO NOT ENGAGE THEM! I have had some encounters with them in the past and they will try to bait you. Don’t give them the time of day. They are not worth it.
If you see anything suspicious PLEASE DO NOT TOUCH IT. Call 911 or if you see a Police Officer let them know.
Together we will get through this. Thank you so much for your support of the Annual Remembrance Day Parade and we look forward to seeing you there!”

Tensions over monuments or statues of Confederate soldiers in public spaces have been high since last summer when white nationalists marched in Charlottesville, Virginia with torches to protest the proposed removal of a statue of Gen. Robert E. Lee.

The violence following the protest left one person dead and dozens injured and sparked protests across the country leading to statues, monuments or markers in places such as Baltimore, Knoxville, Madison, St. Petersburg and New Orleans either toppled, defaced or shrouded ahead of being removed by town councils.

Two state troopers also lost their lives when their helicopter crashed as they were observing the Charlottesville events.

Sunday marks the 154th anniversary of Abraham Lincoln giving his Nov. 19, 1863 speech just months after the battle ended in July. Over 70,000 Confederate troops had engaged 83,000 Federal troops in the battle that would ultimately claim over 50,000 souls and 3,000 horses; it was the battle that changed the course of the war in the Union's favor.

The Gettysburg National Military Park has monuments and memorials to soldiers and units who fought and died during the Battle of Gettysburg, which of course includes both Union and Confederate memorials.

There are over 1,300 monuments, markers and plaques here that reflect the 1863 clash between both sides and the park noted last summer it had no plans to remove any of them through the parks spokesperson Katie Lawhon.