LONDON (AP) — An artwork featuring the plaster face casts of hundreds of transgender people went on display Wednesday in London’s Trafalgar Square, where their features will be worn away by London’s wind and rain over the next 18 months. Mexican artist Teresa Margolles’ “Mil Veces un Instante (A Thousand Times in an Instant)” is a 3.3-metric-ton (3.

6-US-ton) cube covered in face masks of 726 trans, nonbinary and gender nonconforming people. It’s the latest artwork placed atop the “ ” a large stone pedestal in the central London square. Margolles, who trained as a forensic pathologist and once worked in a morgue, has used blood and material from crime scenes in .

The new sculpture evokes a Tzompantli, a rack used in Mesoamerican civilizations to display the skulls of captured enemies and sacrifice victims. It pays tribute to one of the artist’s friends, a transgender woman named Karla who was killed in Ciudad Juárez, Mexico in 2015. The crime remains unsolved.

“We pay this tribute to her and to all the other people who were killed for reasons of hate,” the artist said. “But, above all, to those who live on, to the new generations who will defend the power to freely choose to live with dignity.” Organizers of the project say the work will “naturally age” while on display, with the detail of the faces slowly fading as the plaster is exposed to the elements.

One of London’s main gathering spots for tourists and protesters, Trafalgar Square was .