Bomb casing, from the Haymarket Riot, 1886 (lead)

The Haymarket affair (also known as the Haymarket massacre or Haymarket riot) was the aftermath of a bombing that took place at a labor demonstration on Tuesday May 4, 1886, at Haymarket Square in Chicago. It began as a peaceful rally in support of workers striking for an eight-hour day and in reaction to the killing of several workers the previous day by the police. An unknown person threw a dynamite bomb at police as they acted to disperse the public meeting. The bomb blast and ensuing gunfire resulted in the deaths of seven police officers and at least four civilians; scores of others were wounded.