After they died, the wealthiest and most prominent residents of 18th-century Vilnius, Lithuania, were interred beneath the Dominican Church of the Holy Spirit, in the center of town. Decades later, they were joined by the bodies of Napoleonic troops who had perished while headed home to France after their defeat in Russia.

The tombs were also employed by the living. When Vilnius was overrun by the Polish army in World War I, and by the Nazis in World War II, when the crypt was used as a bomb shelter. But the ᴅᴇᴀᴅ bodies inside endured—even when the Soviets tried to turn the hidden cellars into a museum celebrating atheism.

“Those people buried there were resting and at the same time were witnesses to the historical events that characterized this city,” says Italian anthropologist Dario Piombino-Mascali, who has been studying the remains for five years.

More than half the bodies in the Lithuanian crypt quickly decomposed, leaving behind nothing but skeletal remains. But for some reason—perhaps the season of their death combined with the consistently dry underground climate—other bodies dried out and naturally turned into mummies. Instead of becoming skeletons, skin survived intact and facial features remained recognizable.

In fact, 23 of the crypt’s mummies remain in pristine condition. Piombino-Mascali, a National Geographic grantee, put them in a CT scanner, seeking to learn more about life and health in the 18th and 19th centuries. The mummies are just as important as those from ancient Egypt, he says, because they allow scientists to compare current health issues with those of the not-too-distant past.

Before Piombino-Mascali’s findings, clogged arteries were seen largely as a disease of modernity, though hardened arteries had been seen in Egyptian mummies. Indeed, the Vilnius mummies bear the signs of obesity and sedentary lifestyles.

Most of the corpses also showed signs of cavities in their teeth. And several clearly endured tuberculosis. One young girl suffered from a birth defect and a bone-altering vitamin deficiency that might have been born of her family’s shame.

The people of Vilnius used to think the crypts were haunted, believing that many of the corpses were victims of plague, and that the disease could spread to the living. Piombino-Mascali, who has also led research on mummies in Sicily, says his work has given Vilnius’s residents a more realistic picture of the crypt and their own history.

Here are some of Piombino-Mascali’s creepiest pictures from the project.