“The time will come when our silence will be more powerful than the voices you strangle today,” August Spies said, standing under a gallows in a courtyard of the old Cook County Jail on Hubbard Street.

In the 135 years since his execution, that prophecy has been redeemed around the world. In 1924, the English novelist D.H. Lawrence was in a Mexican village where a monument was being dedicated to the “Martyrs of Chicago.” The peasants had a sense of comradeship with Spies and three other radical activists hanged for a crime they didn’t commit: the deadly bombing of an 1886 union rally in Chicago.

It’s safe to say that scarcely a Chicagoan today could place Spies’ name. Or knows why last Sunday, May 1, was celebrated by marchers elsewhere but not in Chicago, where the May Day workers’ holiday was born.

Yet labor history has a piquant appeal now that some Amazon warehouse workers and Starbuck’s baristas have voted for union representation. They share a common theme with the story of yesteryear militants — a gritty determination to organize the supposedly unorganizable: unskilled workers fearful of risking the little they have.

Even the best-paid workers were slow to organize because American courts frowned on unions. But Chicago was a city of immigrants who gave it a foretaste of European politics. Accordingly, its labor history is replete with dramatic moments and tragic scenes.

At the 1905 founding of the Industrial Workers of the World, Big Bill Haywood, a hard-rock miner, banged a two-by-four on the podium in Brand’s Hall, at Clark and Ontario streets.

“Fellow workers,” he proclaimed. “This is the Continental Congress of the working class.”

On Memorial Day in 1937, striking workers clashed with police at the Republic Steel plant on the South Side. Ten demonstrators were killed and 60 were injured, as were 60 police officers.

The Tribune attributed the violence to “a plan to seize control of the country in the manner of the Russian Revolution.” But a clergyman who conducted the workers’ funerals saw it differently.

“The men lying here had a dream of brotherhood,” the Rev. William Waltmire said. “They sought to bring a new world, a world in which men could live and be happy.”

Chicago witnessed many chapters of labor history after the preface was written at the intersection of Randolph and Des Plaines streets in 1886.

Union activists and militants had called for the nation’s workers to demand an eight-hour day by walking off the job on May 1. At the time, 10- and even 12-hour workdays were common.

“No smoke curled up from the tall chimneys of the factories and mills, and things had assumed a Sabbath-like appearance,” the Tribune reported during the ensuing strike.

Upward of 80,000 marchers paraded peacefully down Michigan Avenue.

But on May 3, the police shot at picketers at the McCormick Reaper Works, and militants called for a demonstration the following day, in Haymarket Square at Des Plaines and Randolph.

Fiery speeches were made by Spies, an upholsterer who edited a socialist newspaper, and Albert Parsons, a leader of the anarchists’ International Working People’s Association.

But the crowd was orderly and thinning out when a bomb was thrown. The police fired back wildly, it was getting dark, and seven officers and anywhere from four to eight civilians were killed.

Newspapers across the nation demanded quick retribution: “Chicago should hang its Socialist Spies and his Parsons with him,” the Omaha Herald wrote.

A Chicago jury convicted Parsons, Spies and six more radicals — including the man officials alleged threw the bomb, who hadn’t even been at the rally.

In 1893, Gov. John Peter Altgeld found that the jurors were selected by a special bailiff who boasted the defendants “would hang as sure as death.” Four had already been hanged when Altgeld freed the others from prison.

Because that miscarriage of justice was associated with the 1886 march in Chicago’s Haymarket Square, May Day became the international worker’s holiday, except in America. But the Haymarket tragedy was still freshly engraved in Chicagoans’ minds when the American Railroad Union held its 1894 convention in Ulrich’s Hall.

There was a bitter strike just south of Chicago. But Eugene Victor Debs, the union’s founder, wasn’t inclined to get involved. Then Jennie Curtis, an 18-year-old, striker addressed the convention.

“We struck at Mr. Pullman because we were without hope,” she said. “And thus the merry war — the dance of skeletons bathed in human tears — goes on, and will go one forever, brothers, unless you, the American Railroad Union, stop it, end it, crush it out.”

The delegates voted to boycott the sleeping cars built in the model town George Pullman named for himself. He was both his workers’ employer and their landlord.

His business hit by a Depression, Pullman cut wages but refused to lower rents. “I have seen men with families of eight or nine children to support, crying because they only got three or four cents after paying their rent,” a Pullman worker told federal investigators.

Army detachments moved into Chicago’s blue-collar neighborhoods when 700 railroad cars in a switching yard were torched by rioters. Debs was jailed by a federal judge who ruled the strikers were preventing the mail from being delivered.

The strike collapsed, taking the union with it. But when Debs returned from the McHenry County Jail in Woodstock, 100,000 workers reportedly greeted him at the Chicago train station. Elected officials were “men with heads as small as chipmunks and pockets as big as balloons,” Debs told that sea of admirers. “The corporation ruled in courts and legislative halls as the fabled bull ruled in a china shop.”

Debs shortly became a Socialist. Like-minded dissenters made pilgrimages to the Haymarket Martyrs burial site in Forest Home Cemetery in suburban Forest Park, and some chose it as their final resting place. The gravestones of its Radicals Row read like an index to the history of the American Left.

Emma Goldman’s is inscribed: “Liberty will not descend to a people, a people must ascend to liberty.” A pioneering feminist, she championed a woman’s economic equality and sexual freedom. Deported during the Red Scare after World War I, the Haymarket Martyrs were her role models.

The lover she left behind, Dr. Ben Reitman, ran a medical clinic for Chicago’s prostitutes and a Hobo College, where university professors lectured skid-row denizens. His headstone reads, “Liberty was his life. Liberty in thought, word, and deed.”

Eddie Balchowsky’s marker is signed: “Your family, friends and fellow ‘premature anti-fascists’ salute you.” The enigmatic phrase was a put-down for those who opposed 1930s dictators while America looked the other way. Balchowsky lost a forearm while serving in a brigade of foreign volunteers who fought for democracy during the Spanish Civil War. In Chicago’s dive bars and folk music clubs he played Chopin’s sonatas with his left hand.

Elizabeth Gurley Flynn’s gravestone is inscribed: “The Rebel Girl.”

She fought for poor people’s rights and free speech but was kicked out of the American Civil Liberties Union for being a Communist. She was sent to prison for the same reason. At her 1952 trial, she acted as her own lawyer.

She noted the government’s case rested not on something she did, but on ideas she’d championed.

“We hold that political theories are not triable in a court of law under our established American tradition, “she argued. “No jury’s verdict can decide their merit; only the people can do that.”

She echoed one of the Haymarket Martyrs. “Oh, men of America!” Albert Parsons said, standing under a gallows on Hubbard Street.

“May I be allowed the privilege of speech even at the last moment? Harken to the voice of the people —”

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