In the late 18th century, wax artist Marie Tussaud launched a somewhat unusual career in Paris. As a forced show of her loyalty to the French Revolution, she was ordered to create death masks of the guillotined aristocrats of the former monarchy, including her onetime employers: King Louis XVI and Marie Antoinette.

Death masks date back to ancient Rome and Egypt, when they were used to preserve the faces of the dead prior to the advent of photography. Through the ages, they’ve been used for funerary rites, portraits, religious ceremonies, and even crime scene investigations.

While Tussaud may not have invented the death mask, she was the first to commercialize the ancient practice on a massive scale. In 1802, after the conclusion of the Revolution, she took her waxworks collection on a traveling show through Britain and eventually settled on London’s Baker Street in 1835. The exhibition expanded to include English royalty, famous political figures, and dioramas of notorious criminals and their gruesome crime scenes.

In an effort to make the waxworks as authentic as possible, business savvy Tussaud secured original artifacts to embellish her graphic tableaux—from the pram used to transport the dismembered remains of the 1890 Hampstead murder victims to King George IV’s glittering coronation robes.

View Images Crowds of people queue outside of Madame Tussauds on a rainy day in London circa 1930. Photograph by Topical Press Agency/Getty Images

London’s Punch magazine soon coined it the “Chamber of Horrors,” a moniker that stuck. News of Madame Tussauds tore through London and the business boomed, appealing to the public’s most morbid curiosities.

But with success came controversy. Commentators argued that using tragedy for public spectacle was distasteful and sensationalistic—a criticism that followed the collection through the centuries despite its continuing popularity.

Today millions of visitors continue to trek to Tussauds locations in 24 cities across four continents. While the museum’s studio still employs some of the original techniques used by Tussaud, the glossy figures of Hollywood starlets, professional athletes, and infamous politicians are often fashioned from the living.

View Images A cameraman films a pair of women as they craft waxwork heads for a new exhibition at Madame Tussauds London in 1928. Photograph by Console/Topical Press Agency, Getty Images

The months-long process begins with a meticulous series of photographs and measurements from which a sculptor models a clay figure. Once finished, a caster pours a wax mold; color specialists carefully match the tones of the skin, teeth, and eyes; and real human hair is inserted individually into the head, eyelashes, and eyebrows. Each piece runs a bill of more than $186,000 (£150,000)—like a recent sculpture of President Donald Trump that took five months and 20 artists to complete.