On July 21st 1877, the Philadelphia militia fired into a vocal crowd of striking Pennsylvania trainmen and sympathizers. Twenty people were killed, including at least three children. Many more were wounded. Following the attack, the militia retreated to the roundhouse at 26th Street and Liberty Avenue as family, friends and neighbors prepared to avenge the dead.

While the tired and hungry militia hunkered down inside, a howling mob began to assemble outside the roundhouse. Accompanied by drums and fifes, the crowd aimed stones, bricks, and bullets at the doors and windows. Unable to flush the militia out of the roundhouse, the mob set fire to freight cars carrying coal, oil, whiskey and wine. The flaming cars were sent careening down the Liberty Avenue tracks, into the roundhouse. As flames engulfed the building, General Brinton and his troops evacuated on the morning of July 22nd. Using rifles and two Gatling guns to sweep their path, the militia killed an additional 20 civilians while retreating eastward out of the city.