Boston police estimated that almost 40,000 demonstrators total at the rally.
Aerial photos showed counter- protesters filling one of Boston's main streets for several blocks, in a huge outpouring of anti-racist sentiment in this strongly Democratic north-eastern city.
Thousands of people poured onto the streets of Boston to demonstrate against racism and hate, one week after race-related protests turned violent in Charlottesville.
Although city officials had asked counter-protesters to stay away, saying their presence would draw more attention to the far-right activists, the group was later commended for standing up to hate and bigotry during the largely peaceful day.
"The fight over symbolism that pays homage to the Confederacy gained increasing momentum over the week after President Donald Trump criticized protesters "on both sides" of the battle", all but defending the white nationalists who have vowed to, as they shouted in Charlottesville, "unite the Right".
"It was attractive to see thousands of people across the United States of America come together today to peacefully denounce bigotry, racism & anti-semitism", she tweeted Saturday, following numerous demonstrations across the country against white supremacy.
Ms Trump, 35, ensured she couldn't be accused of making an equivalence between white supremacist groups and counter-demonstrators by tweeting: "It was attractive to see thousands of people across the U.S.A come together today to peacefully denounce bigotry, racism & anti-semitism". Most of the arrests were for disorderly conduct.
Thousands of counter-protesters had convened in two groups before the main rally, chanting "No Nazis, no KKK, no fascists in the U.S.!" Cohn, who also flanked the president at the Trump Tower event, will remain in his position, a White House official said on Thursday. "We are out here to add an extra body to add to the numbers of those who resist".
Last weekend's violent clashes in Charlottesville, Virginia, where one woman was killed in a vehicle rampage after bloody street battles, ratcheted up racial tensions already inflamed by white supremacist groups marching more openly in rallies across the United States.
Wow.Protestors surround two men in Trump gear and scream profanities, tell them to get the f*^% out of Boston.
According to an AFP photographer at the scene, police in riot gear prevented counter-protesters from reaching the venue of the white nationalist rally-leading some to accuse police of defending "Nazis".
Some of Trump's comments, criticising "alt-left" protesters as "very, very violent", came on August 15th with Mnuchin standing by the president's side in the lobby of Trump Tower in NY. "Love, no hate", he added.
It's a great feeling watching Nazis and white supremacists fail. "This is our solidarity with the people in Charlottesville, Virginia, as well as a notice to our local leaders that we want all statues dedicated to white supremacists taken down".