Editor's Note: This report was first published in 2010. We've pulled it up from our archives to provide historical background on the annual commemoration.
Workers in scores of nations each year mark the first of May. Socialists and practicing communists wave red banners in the streets.
Throw in a few anarchists and you have the makings of May Day, the traditional International Workers' Day celebrated around the world.
But did you know that they are commemorating an event which occurred in Chicago, 124 years ago?
That event was what has become known as the "Haymarket Massacre," and it looms larger than life for millions of workers all over the globe.
"This is not just an event, over a hundred years ago," said historian Peter Alter at the Chicago History Museum. "This is an event that still has resonance today."
It started with a demonstration for an eight-hour day at a McCormick reaper plant on Chicago's Southwest side on May 3, 1886.
Several of the demonstrators were killed, and workers planned a massive rally in Haymarket Square on the city's west side for the following night.
"There were anarchists there, there were socialists there," said Alter. "There were good old bread and butter unionists there."
It was planned as a rally for 25,000 people, but probably only a tenth of those showed up. Mayor Carter Harrison visited and left.
Most of the crowd, in fact, was starting to drift away when scores of police suddenly showed up, demanding that the remaining onlookers disperse. At that moment, someone stepped out of an alley near Des Plaines and Randolph streets and threw a bomb into the crowd.
There was a massive explosion and a flurry of gunfire.
When the melee had subsided, at least seven policemen and four of the demonstrators were dead. About 60 more police were wounded. Some commanders at the time speculated that many of the officers' wounds came from friendly fire in the confusion. (One officer died from his wounds two years later). But the public, and especially Chicago's business leaders, were outraged at the carnage, and called for swift action.
Martial law was declared in the city. Labor leaders were rounded up, including those who were deemed responsible for the rally.
Eight men were eventually charged with inciting what was referred to as the "Haymarket Riot." On August 20, 1886, seven of the eight defendants received death sentences.
The Chicago Times described the defendants as "arch counselors of riot, pillage, incendiarism and murder." Other papers called the alleged plotters "red ruffians" or "bloody monsters."
Two would see their sentences commuted to life and one killed himself in his cell. The remaining four defendants were hanged in the courtyard of the Criminal Courts Building at Dearborn and Hubbard on November 11, 1887.
On the gallows, defendant August Spies declared, "The time will come when our silence will be more powerful than the voices you strangle today."
The Haymarket defendants are buried together beneath a monument constructed in 1893 in Waldheim Cemetery in suburban Forest Park. That same year, Illinois Governor John Peter Altgeld signed pardons for the three defendants who had drawn life sentences, concluding all eight defendants were innocent.
The bomb thrower has never been identified.
"Certainly there was very limited evidence against the men who were executed," said Alter. "Some of them were not there! Some of them were only loosely affiliated. What they were tried for, were their points of view."
Two years later, the first congress of the Second International, meeting in Paris, called for worldwide demonstrations in 1890 on the anniversary of the Chicago protests.
May Day became formally recognized the following year and over the decades became a focal point for demonstrations by workers and labor organizations, as well as various socialist, communist, and anarchist groups around the world.
"It is sacred to the cause of advancement of the working man around the country," says labor activist Les Orear. "It was such a tragedy, with the interference to the right to free speech, free assembly, our own first amendment."