Earlier this week, Islamic State militants publicly destroyed more priceless relics in the ancient city of Palmyra in Syria, reports the Washington Post. Today, the group released a video showing it making use of the city in an even more heinous way—to stage a mass execution of Syrian soldiers, reports the BBC. The video shows about 25 men being shot to death in the Palmyra amphitheater—by gunmen who appear to be about 13 or 14 years old. Militants reportedly forced hundreds of local residents to witness the killings. As the Huffington Post notes, a group of Syrian soldiers were reportedly executed at the site in late May, and this may be the video of that slaughter. (More Islamic State stories.)