Gun control activists arranged 7,000 pairs of shoes on the lawn of the U.S. Capitol building Tuesday to honor victims of gun violence, Reuters reports. Each pair of shoes represents one child killed by a gun since the Sandy Hook massacre in 2012.

Twenty children and six adults were killed in the Sandy Hook shooting, and, at the time, many gun control activists believed the tragedy would spur legislators into action on the issue of gun control. 

However, that wasn't the case. Now, fresh off the high school shooting in Parkland, Florida, which left 17 dead and it has sparked protests from students nationwide.

Civic organization Avaaz, the National School Walkout, and other gun control activists decided to represent this issue in plain sight, in a way lawmakers couldn't avoid.

“This is really about putting the human cost of refusing to pass gun control at the doorstep of lawmakers,” said Emma Ruby-Sachs, deputy director of Avaaz. “I think we’re in the middle of a cultural change in the United States. The majority of Americans want a change in gun laws, and a majority of gun owners want change.”

According to the U.S. Centers for Disease Control and Prevention, approximately 1,300 of people under the age of 18 are killed by guns every year. 

Tom Mauser, one of the volunteers who helped to set up the action, knows the cost of gun violence personally. In 1999, his 15-year-old son Daniel was killed in the shooting at Columbine High School.

Explaining the meaning behind the installation, he said, “There’s nobody in those shoes, it’s like the emptiness in our hearts from gun violence.”

The display wasn't limited to the shoes, as around it protesters held signs with messages like “#NOTONEMORE” and “7,000 KIDS KILLED." 

More protests are to come. On Wednesday the activists who assisted in planning the Women's March in Washington, D.C., will host the #ENOUGH National School Walkout, which will begin at 10 a.m. local time. On March 24, student advocates for stronger gun control laws from across the U.S. will march on the nation's capital in the March For Our Lives.