The third cholera pandemic in recorded history—and the deadliest—began in India sometime in the mid-1800s, making its way across Asia, Europe, Africa, and the Americas throughout the 1850s. By the time it subsided in 1860, the pandemic had killed more than a million people around the world—which, luckily for Clark Larsen, included the victims buried in the mass grave at Badia Pozzeveri, an ancient church in the small town of Altopascio, Italy.

For the past three years, Larsen, a professor of anthropology at the Ohio State University, has helped to lead a team of archaeologists as they sift through a corner of the cemetery known as “Area 2000,” searching for clues to the evolution of the disease.

For six weeks each summer, the Field School at Badia Pozzeveri, a collaboration between Ohio State and the University of Pisa, gives students a chance to excavate the site’s human remains, which stretch back as far as the bubonic-plague outbreak that devastated Europe in the 14th century. The discovery of the grave—which Larsen estimates contains “a couple hundred” bodies—was a happy accident during a dig in the summer of 2012, as Science magazine reported the following year; old records confirmed that the victims had died of cholera when the epidemic swept through Tuscany in 1855.