Rep. John Lewis, D-Georgia, appeared on the Capitol steps along with Rep. Cedric Richmond, D-Louisiana, Rep. Maxine Waters, D-California, Rep. Greg Meeks, D-New York, Rep. Sheila Jackson Lee, D-Texas, and Rep. G.K. Butterfield, D-North Carolina, to speak to the crowd of protesters who marched from the White House to the Capitol building.
Lewis, a civil rights icon, was the first to address the crowd, using a bullhorn to be heard over the gathering.
"We want to thank you, because when you see something that is not right, not fair, not just, we have a moral obligation to stand up," Lewis said.
Lewis reminded the crowd he once led marches for the civil rights movement alongside Dr. Martin Luther King Jr.
"I went to jail 40 times during the '60s. I was left bloody and unconscious. But I never gave up. I never gave in. You never give in, never give up," Lewis said.
At times, Lewis was interrupted by chants of "black lives matter," causing some demonstrators to urge them to let Lewis finish speaking.
"What we see tonight is the beginning of a great movement," said Butterfield, the chairman of the Congressional Black Caucus, who vowed to "beat up Republicans" until they take up a bill to address gun control.
The crowd broke out in cheers when Waters echoed the crowd's sentiment, saying, "I am sick of this s--- and I'm not going to take it anymore."
After Waters finished speaking, the crowd slowly began to march back to the White House. At times, they chanted, "hands up, don't shoot," "no justice, no peace," and "hey, hey, ho, ho / these racist cops have got to go."
Capitol Police spokeswoman Eva Malecki said one person was arrested at the Capitol for crossing a police line.
Americans across the nation vented their anger over the police killings of two black men in two days.
They chanted outside the governor's residence in St. Paul, Minnesota, miles from the spot where an officer killed Philando Castile in a car
on Wednesday while a 4-year-old girl sat in the back seat.
Crowds milled in the streets outside the convenience store in Baton Rouge, Louisiana, where Alton Sterling was fatally shot
while police grappled with him in a parking lot Tuesday.
Protesters briefly shut down the Dan Ryan Expressway in Chicago. In New York, 1,000 people marched down Fifth Avenue and a few scuffled with police officers.
And in Dallas, several police officers were shot and killed
during a protest.