Protesters with the Black Lives Matter movement briefly shut down a major highway in the nation’s capital Saturday afternoon as part of Blackout DC, a demonstration against racial discrimination. Hundreds of activists blocked traffic on Interstate 395 en route to the Capitol.

Videos on Twitter showed protesters walking between cars in the road, raising their fists and shouting, “Black lives matter.” Several drivers could be heard honking in rhythm with the chants.

Blackout DC aimed to raise awareness for “black unity, equality and strategies to combat state-sanctioned, racially motivated violence against black people,” according to a crowdfunding profile set up by the organizers. A Facebook page for the event showed more than 480 people planned to participate.

Among those in attendance was Deray McKesson, a high-profile activist who was arrested earlier this week in Ferguson, Missouri, where protesters assembled for the one-year anniversary of the police shooting death of unarmed black teen Michael Brown. Singer Janelle Monae was nearby Saturday, holding her own demonstration against police brutality at the U.S. Department of Justice headquarters.

#BlackoutDC trended nationally on Twitter as dozens of people posted photos and messages about the protest. Many showed the crowd that assembled outside the Capitol while others relayed the phrases on activists’ signs: “Stop racist police terror,” “Black skin is not a sin” and “I’m not a target” were among them. Some users tweeted out phone numbers for legal support should marchers be arrested.

Black Lives Matter events have picked up over the past week as people across the country remembered Brown, whose 2014 death sparked outcry over what many called institutionalized racism. About 150 protesters came out Monday night in Ferguson, some of them confronting police and throwing rocks and water bottles. St. Louis County instituted a state of emergency that was lifted Friday.