Chicago's Haymarket affair turned deadly

On the evening of 4 May 1886, around 1,500 workers gathered on Desplaines Street in Chicago, in the district known as Haymarket Square. The meeting had been called to protest a deadly clash the previous day at the McCormick reaping works, part of a wider national push for an eight-hour workday.

The crowd had thinned and rain was falling when police moved in to break up the remaining speakers. At that moment, someone hurled a dynamite bomb into the ranks of officers. In the blast and the gunfire that followed, seven police officers and at least one civilian were killed, and roughly sixty more people were wounded. The identity of the bomber has never been established.

No evidence tied the accused to the device, yet eight known anarchists were charged. The trial, widely seen as driven by their politics rather than proof, sent four men to the gallows and turned Haymarket into a lasting symbol of the international labor movement — and of May Day itself.