May Day first started in Ancient Rome, where it was celebrated in order to honor Flora, the Goddess of fertility, flowers, and spring. The festival was a chaotic ordeal. The United Kingdom’s National Trust, a conservation charity that looks after nature, beauty and history for everyone states that the ancient Romans celebrating the holiday were "notorious for lewd behavior. Vegetables were pelted and wild hares and deers were released into the crowds as symbols of fecundity.” The festivities spanned from Apr. 28 to May 3. The festival began as a whole ordeal that included athletic competitions and theatrical performances. 

Hundreds of years later, the Haymarket Affair takes place in Chicago, Illinois. The Affair quickly became known as May Day and as the first International Labor Day. The Flowery May Day and the Haymarket Affair May Day are not one in the same, but share the same name.

The Haymarket Affair was a multi-day protest for labor rights that quickly turned violent. The protests took place from Apr. 25 to May 4, 1886, and a variety of different people involved themselves in the movement: unionists, socialists, anarchists, reformers, and workers. On May 1, around 35,000 workers of different skill ranges walked out. As the group walked, they urged others to join their strike. The police crashed with the protests at least 12 times; three of them ended with a shooting. On May 3, the police killed two protestors and the anarchists called for a gathering the next day at the West Randolph Street Haymarket. The Mayor, Carter H. Harrison, urged the police not to involve themselves. However, Inspector John Bonfield and 172 other officers did not listen. The protest quickly escalated. One of the protestors hurled a bomb at the police, killing one officer instantly. At the end of everything, sixty officers were injured and eight were killed. An unknown number of protesters were injured or killed. Hundreds of protestors were arrested; however, the bomber was never identified. 

Even though the bomber remained a mystery, eight anarchists were arrested and tried for murder. The trial was bogus-- it had a partisan judge and twelve jurors who claimed prejudice against the defendants. According to the Encyclopedia of Chicago, the trial lacked “credible evidence that the defendants threw the bomb or organized the bomb-throwing, prosecutors focused on their writings and speeches.” All eight were convicted, and seven were sentenced to death. Americans were outraged by the trial and managed to get two death sentences rescinded. Though a year later on Nov 11, 1887, four of the anarchists were hanged and another committed suicide. The governor, John Peter Altgeld pardoned the remaining anarchists on the grounds of a lack of evidence and an unfair trial. 

Sources:

• The National Trust

• The Library of Congress

• Historic UK

• Encyclopedia of Chicago