Dakota Native Americans held a ceremony in Minnesota on Wednesday to commemorate the 150th anniversary of the largest mass execution in U.S. history. Thirty-eight Dakota men were hanged simultaneously on December 26, 1862, in front of thousands of onlookers. They were condemned to death for crimes allegedly committed during a brief, but bloody war with white settlers and soldiers. The executions were allowed by then-President Abraham Lincoln, despite sparse evidence. The conflict came amidst broken U.S. treaties and desperate conditions that left some Dakota starving. After the war, nearly 2,000 Dakota noncombatants were marched to a prison camp where as many as 300 died. Some Dakota marked Wednesday’s anniversary with an annual 300-mile horseback ride ending with the unveiling of a public memorial in Mankato, Minnesota, the site of the executions.