Illustration by Patrick O’Brien

May 31, 1889. The rain was pounding. Victor Heiser,16, sloshed through knee-deep water to the barn behind his home. Victor and other people in Johnstown, Pennsylvania, were used to seeing the Conemaugh River, which runs through town, overflow its banks in the spring. But they had no idea what was about to hit them. In the barn Victor untied the horses. As he turned to leave, he heard a fearsome roar. He froze.