Tens of thousands of people took to the streets of Boston on Saturday to protest a “free speech” rally featuring far-right speakers a week after a woman was killed at a Virginia white-supremacist demonstration.

Rally organizers had invited several far-right speakers who were confined to a small pen that police set up in the historic Boston Common park to keep the two sides separate. The city avoided a repeat of last weekend’s bloody street battles in Charlottesville, Virginia, where one woman was killed.

Police estimated that as many as 40,000 people packed into the streets around the nation’s oldest park.

Officials had spent a week planning security for the event, mobilizing 500 police officers, including many on bikes, and placing barricades and large white dump trucks on streets along the park, aiming to deter car-based attacks like those seen in Charlottesville and Europe.

The rally never numbered more than a few dozen people, and its speakers could not be heard due to the shouts of those protesting it and the wide security cordon between the two sides. It wrapped up about an hour earlier than planned.

Protesters surrounded people leaving the rally, shouting “shame” and “go home” and occasionally throwing plastic water bottles. Police escorted several rally participants through the crowds, sometimes struggling against protesters who tried to stop them.

Some people dressed in black with covered faces several times swarmed rally attendees, including two men wearing the “Make America Great Again” caps from President Donald Trump’s campaign.

The violence in Charlottesville triggered the biggest domestic crisis yet for Trump, who provoked ire across the political spectrum for not immediately condemning white nationalists and for praising “very fine people” on both sides of the fight.

On Saturday, Trump on Twitter praised the Boston protesters.

“I want to applaud the many protesters in Boston who are speaking out against bigotry and hate. Our country will soon come together as one!” Trump tweeted. “Our great country has been divided for decades. Sometimes you need protest in order to heal, & we will heal, & be stronger than ever before!”

Thirty-three people were arrested, largely for scuffles in which some protesters threw rocks and bottles of urine at police dressed in riot gear, the Boston Police Department said.

“There was a little bit of a confrontation,” Police Commissioner William Evans told reporters, adding that “99.9 percent of the people who were here were here for the right reasons.”

-Reuters