Protesters left 7,000 pairs of shoes in front of the Capitol building Tuesday to symbolize the number of children killed by gun violence in the United States since the Sandy Hook Elementary School shooting in December 2012.

From 8:30 am to 2 pm, the shoes were displayed on the southeast lawn in the hope of sending a clear message to Congress: Reform gun control legislation or more children will be killed by gun violence.

The global advocacy group Avaaz — a US-based organization launched in 2007 that promotes global activism on issues such as climate change, human rights, animal rights, corruption, poverty, and conflict — planned the protest, which meant finding a way to collect 7,000 pairs of shoes.

Avaaz’s website says the group received donations from victims’ families, members of the public, and even celebrities.

“Ahead of the March for our Lives, this monument is bringing the heartbreak of gun violence directly to congress’ doorstep,” Avaaz wrote in a press release announcing the protest.

The event comes amid a wave of gun control activism in the wake of last month’s shooting at Marjory Stoneman Douglas High School in Florida, including the National School Walkout planned for Wednesday, March 14, and a march on Washington scheduled for March 24.