The 1955 murder of Black teenager Emmett Till in Mississippi by white assailants is one of the 20th century’s great tragedies, an act of violence so shocking that it helped spark the modern civil rights movement. Following her son's death, Mamie Till-Mobley demanded justice and societal change.

Mobley died in 2003, but her voice is still being heard. On Tuesday, as The New York Times reports, President Joe Biden signed a proclamation that will formally establish three sites across Mississippi and Illinois as the Emmett Till and Mamie Till-Mobley National Monument.

Till, 14, was kidnapped by Roy Bryant and J.W. Milam after the two men were angered over Till’s alleged comments toward Bryant’s wife while Till was visiting relatives in Mississippi; she also stated Till grabbed her. The men beat and murdered Till, then left his body in the Tallahatchie River. They were acquitted by an all-white jury, though both later admitted to killing the child in an interview. The woman, Carolyn Bryant Donham, later admitted that her testimony about Till physically touching her was untrue.

The proclamation identifies Graball Landing in Tallahatchie County, the site where Till’s body was discovered in the Tallahatchie River; Roberts Temple Church of God in Christ, the Chicago church where Till’s funeral was held; and the Tallahatchie County Second District Courthouse in Sumner, where Till’s killers were tried. All will fall under the purview of the National Park Service.

Following Till’s death, Mamie Till-Mobley waged a battle to have the country bear witness to the horror of the racist crime. She insisted Till have an open-casket funeral so his injuries would be visible. She also wrote to President Dwight Eisenhower pleading for federal intervention in her son’s case. The injustice helped stoke civil rights action. Rosa Parks later cited Till’s murder as one of the reasons she asserted herself on a bus in Montgomery, Alabama, by refusing to stand so a white passenger could sit.

Biden also signed a bill passed in the House that will posthumously give Congressional Gold Medals to Mamie Till-Mobley and her son. Tuesday would have been Emmett Till’s 82nd birthday.

This article was originally published on www.mentalfloss.com as A National Monument Has Just Been Established to Honor Emmett Till and Mamie Till-Mobley.