May 1, at once a flower festival older than Rome and the workers' holiday born from a Chicago bomb.
Documented
Haymarket
In May 1886 Chicago police fired on striking workers fighting for the eight-hour day, and a bomb at Haymarket Square killed officers and civilians. Four anarchists were hanged on evidence even contemporaries called weak. International labor adopted May 1 to honor them, and today more than sixty countries mark it.
Assessment: Documented: trial records, the 1886 strike, and the global calendar all check out.
Stories
The older May
Long before unions, May 1 was Beltane fire festivals, Roman Floralia, maypoles and May queens: the hinge between winter and summer. The labor movement did not pick the date at random; it parked its grief on a day people already took off.
Assessment: Stories: the spring festival is genuinely ancient, the fusion is 1886.
Interesting claims
The American sidestep
The US put Labor Day in September, in part to avoid honoring Haymarket radicals. Meanwhile the distress call mayday is unrelated: it is French m'aidez, help me, coined for radio in the 1920s. Same sounds, three different histories.
Assessment: Interesting claims: the date your country rests is a political choice wearing a calendar costume.
Sources and further reading
Trial and execution records of the Haymarket anarchists, Chicago, 1886-1887; pardoned by Governor Altgeld, 1893, on the trial's injustice
Reportage of the May 1886 eight-hour strikes and the Haymarket Square bombing, Chicago Tribune archives
International Socialist Congress, Paris (1889): the resolution adopting May 1 as international workers' day
Frederick Stanley Mockford's 1923 coinage of the 'mayday' distress call from French m'aidez
Worth asking
Two holidays share one square on the calendar, one flowers and one blood; which one you inherited depends on which argument your country lost.