Faces of transgender people adorn an artwork in London's Trafalgar Square

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 “ Fourth Plinth, ” 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 artworks exploring death and conflict.

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 named for Admiral Horatio Nelson’s 1805 victory over the French and Spanish fleets. A statue of the one-armed admiral stands atop Nelson’s Column at the center of the square, and statues of other 19th-century military leaders are nearby.

The fourth plinth — a 24-foot (7-meter) high stone pedestal -- was erected in 1841 for a never-completed equestrian statue, and since 1999 has been occupied by a series of artworks for about 18 months at a time.

Previous occupants included a giant bronze thumb, a sculpture of a giant swirl of whipped cream topped with a cherry, a fly and a drone, and 2,400 members of the public who each stood atop the plinth for an hour over the course of 100 days.