An illustration depicts the 1886 Haymarket Square riot. - Tribune archive photo

Haymarket Square

On May 4, police officers try to disperse a previously peaceful rally of union activists, socialists and reformers. A bomb is thrown at police, killing one. Police open fire. In the ensuing chaos, eight officers are killed and scores are injured. An unknown number of protesters are killed or hurt. The debate continues today whether the incident at Haymarket Square was a riot, a bombing or a massacre. But it is widely recognized as an inspiration for the establishment of International Workers’ Day, or May Day.