The 2nd, 3rd, 5th, 6th and 7th Wisconsin Infantry regiments fought at South Mountain. Seeing them from a distance, the Union’s top commander, General George McClellan, commented, "They must be made of iron." Historians believe that this was probably the origin of the name, Iron Brigade. When McClellan was told that the brigade had performed even more heroically two weeks earlier at Second Battle of Bull Run, he called them the "best troops in the world." At South Mountain, Wisconsin regiments lost 222 men killed or wounded.