Hundreds of masked anarchists and black bloc affiliates were arrested in Paris on Tuesday, Reuters reported, after rioters burned cars and smashed shop windows during the city’s May Day rally.

What was once an event with roots as a spring festival in European pagan cultures has evolved into an international day of marches in the name of worker rights. But these May Day celebrations have been regularly marred by violence since at least the 19th century, as The Washington Post noted on May 1 last year.

Paris got the worst of it this year. Somewhere between 20,000 and 55,000 marchers gathered in the capital, according to Reuters, intending to march peacefully against President Emmanuel Macron’s plans to roll back labor protections. But about 1,200 “masked and hooded protesters” dressed in black stood on the sidelines, according to the news agency.

Some were anarchists, some waved Soviet flags, and some were antifascists — upset by a gathering of far-right European leaders in France on the same day.

The gathering tipped into violence.

The protesters’ colored smoke bombs mixed in the air with tear gas, water from police cannons and petrol bombs. Before the chaos subsided, vehicles had been set on fire, windows at a McDonald’s smashed out, several shops looted and 200 people detained, Reuters reported.

Four people, including a police officer, reportedly suffered minor wounds.

“When you come with Molotov cocktails, it’s to burn cops,” a police union official said, according to Reuters. He added that the protesters had been allowed to target buildings, lest they be provoked into attacking people.

“Those who wear hoods are the enemies of democracy,” government spokesman Benjamin Griveaux said after the violence, according to Reuters.

The rioting recalled May Day events from two years ago, when people angry at France’s unemployment rate and unpopular socialist president turned Paris’s Place de la Republique into a scene of chaos.

In other countries, demonstrators rallied on Tuesday against perceived injustices.

Large gatherings were planned in cities across the United States to protest President Trump’s restrictive immigration policies, the Associated Press wrote. Thousands of people in the U.S. territory of Puerto Rico marched against the federal government, deeply frustrated that tens of thousands of homes remain without power months after Hurricane Maria hit the island in September.

The AP listed country after country: In Cambodia, garment workers organized the main rally. In Istanbul, police detained protesters and forbade them from marching toward the main square, where 34 people were fatally shot on May Day 1977.

But in Moscow, the AP wrote, it was not a day for outrage. About 10,000 paraded through the Russian capital on May Day in what the news agency called a “show of power by Russian authorities.”

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