In the middle of the night on May 21, a 16-year-old Brazilian girl was repeatedly raped by 33 men, according to her statements to police. It was a particularly heinous instance of a sadly common occurrence in Brazil -- and in much of the world. Rapes are often unreported and their victims silenced -- but in this instance, photos and even a video were uploaded to social media, apparently in some sort of wicked bragging competition.

In the subsequent weeks, thousands of people in Brazil, mostly women, have taken to the streets to protest the culture of rape, and to counter a persistent narrative among politicians, the police and the media that shifts blame onto the victim.

This week, an NGO called Rio de Paz, or "Peaceful Rio," a nod to Rio de Janeiro, the city where the crime took place, staged an eye-catching protest on one of the world's most famous beaches, Copacabana. Scattered among large stylized photographs of women with the mark of a bloody handprint covering their mouths were 420 pairs of underwear. That is the number of women raped every three days in Brazil, the organizers said. The photos, taken by Marco Freitas, are part of an exhibit titled "I will never be silenced."

Below are pictures from the protest:

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