While excavating an ancient Roman villa buried in volcanic ash, 18th-century workers found an unusual lump of metal small enough to fit in a coffee mug. Cleaning it revealed something both historically important and hilarious: one of the world’s oldest known examples of a portable sundial, which was made in the shape of an Italian ham.

Now the “pork clock” ticks once more. Recently re-created through 3-D printing, a high-fidelity model of the sundial is helping researchers address questions about how it was used and the information it conveyed.

The model confirms, for instance, that using the whimsical timepiece required a certain amount of finesse, says Wesleyan University’s Christopher Parslow, a professor of classical studies and Roman archaeology who made the 3-D reconstruction. All the same, “it does represent a knowledge of how the sun works, and it can be used to tell time.”

Telling Tail

The pork clock was excavated in the 1760s from the ruins of the Villa dei Papiri, a grand country house in the Roman town of Herculaneum. Like nearby Pompeii, Herculaneum was destroyed by the catastrophic eruption of Mount Vesuvius in A.D. 79.

Early scholars were quick to realize that the unprepossessing object was a sundial, though some experts argued that it was modeled after a water jug rather than a ham.

The object was the pocket watch of its day. Fixed sundials were everywhere in ancient Greece and Rome, but only 25 other portable sundials from antiquity are known, says Alexander Jones, a historian of ancient science at New York University’s Institute for the Study of the Ancient World, who was not involved in Parslow’s experiments. It’s not clear exactly when the Herculaneum clock was made, but it is either the oldest or second oldest surviving portable sundial, Jones says.

After Parslow was asked about the pork clock, he was inspired to build a 3-D model. He took dozens of photos of the timepiece at its home institution, Italy’s National Archaeological Museum of Naples. A 3-D printer at his university churned out the model—in plastic rather than the original silver-coated bronze—in a matter of hours.

Like the original, Parslow’s model bears a dial, in the form of a slightly distorted grid, on one side. The vertical lines are marked for the months of the year. The horizontal lines indicate the number of hours past sunrise or before sunset.

The original clock is missing its gnomon, the part of a sundial that casts a shadow, but an 18th-century museum curator described it having one in the shape of a pig’s tail, so Parslow re-created that, too.

Parslow then experimented with the sundial outdoors. The clock is hung from a string so that the sun falls on its left side, allowing the attached pig’s tail to cast a shadow across the grid.

The user aligns the clock so that the tip of the tail’s shadow falls on the vertical line for the current month. Finally, the user counts the number of horizontal lines from the top horizontal line to the horizontal line closest to the tip of the shadow. That indicates the number of hours after sunrise or before sunset.

Status Symbol

Once Parslow mastered the clock, which tends to sway in the wind, he could read off the hour. Parslow is now tinkering with the tail’s length and sharpness in new versions of the model to improve its fidelity to the original.

View Images An Italian prosciutto ham is seen hanging for curing and aging. Photograph by Photology1971, Alamy Stock Photo

In theory, the clock’s design allows for telling the time to the half hour, or even the quarter hour. But “the scale of the whole thing is so small, and it is so difficult to hold steady, that such accuracy is likely the theoretical ideal rather than the reality,” says Parslow, who presented his first round of results in early January at a meeting of the Archaeological Institute of America and the Society for Classical Studies.

The object seems impractical, but Romans didn’t need to know the time of day down to the minute. Also, the clock might have been more of a status item, Jones says, like “modern, expensive Swiss watches. You don't just own them to tell time. You own them to show that you own them.”

So why the shape of a prosciutto, the Italian version of a leg of ham? Parslow isn’t sure, but he notes that the pig is a symbol in Epicurean philosophy, which emphasized living for the day. And most of the texts found at the Villa dei Papiri are related to Epicurean philosophy, says Kenneth Lapatin, curator of antiquities at the J. Paul Getty Museum.

“There was a lot of humor among the Epicureans,” Lapatin says, so perhaps the shape is a macabre joke: “Enjoy your life while you’ve got it, because you’re going to end up like a ham.”