At a signing ceremony in Denver Tuesday, Polis reversed orders that were made by Territorial Governor John Evans in 1864, stating that they “shamefully targeted and endangered the lives” of indigenous people.

The proclamations led to the Sand Creek Massacre—one of the deadliest mass murders in American history—in which the U.S. Army attacked Cheyenne and Arapaho people and slaughtered at least 230.

“When then-Gov. Evans made that proclamation, he said, ‘you can hunt Native people,’ just as if you hunted buffalo and antelope and elk and deer—it was open season,” Reggie Wassana, governor of the Cheyenne and Arapaho Tribes based in Wyoming said during the ceremony, according to the Colorado Sun.

Polis said that rescinding the proclamations is part of an “ongoing process to make amends with the sins of the past.” Though the orders were never officially signed into law, the Colorado governor noted that they had never been formally revoked, either.

“We are tearing down this awful symbol of hate,” Polis added during his address, Axios reported.

In 1864, as the Civil War moved into the West, rumors spread that Native tribes in Colorado were allied with the Confederacy to drive white soldiers off the plains, according to the Sand Creek Massacre Foundation. That prompted Evans to issue two proclamations warning that “all hostile Indians would be pursued and destroyed” unless they placed themselves under the protection of the military.

The proclamations also authorized citizens of Colorado “to go in pursuit of all hostile Indians on the plains,” offering those who organized as a militia to be furnished with arms and ammunition.

During that time, over 750 Cheyenne and Arapaho people camped along the banks of Big Sandy Creek in southeastern Colorado, believing they were following Evans’ proclamation and placed under the protection of the U.S. Army, according to the Colorado Sun.

But on November 29, 1864, more than 650 U.S. soldiers carried out an unprovoked attack of the village, killing and mutilating around 230 people. For two days, the troops shot and hunted fleeing women, children and elderly people across a 35-square-mile region.

“It was Native American people protecting our homelands, only to be criticized as negative and hostile,” Melvin Baker, chairman of the Southern Ute Indian Tribe, said during the ceremony Tuesday, according to the Sun.

On Tuesday, a number of representatives and leaders from the Southern Ute, Ute Mountain, Cheyenne and Arapaho Tribes attended the ceremony and noted the symbolism of rescinding the violent orders.

“The truth of this history must be told, and only then can the healing begin. Once there is truth, and documented wrongdoing, there must be reconciliation,” Richard B. Williams, a member of the Northern Cheyenne Tribe, said in a statement Tuesday.

“The honor of the people of the State of Colorado and the Nation is on the line. They failed before but now have an opportunity to help the original inhabitants of the land,” Williams added.

Newsweek contacted Polis’ office for additional comment, but did not hear back in time for publication.