More than 2000 years ago, the Greek philosopher Philodemus (or one of his scribes) painstakingly inked a history of the country’s great thinkers, called History of the Academy, on a giant scroll of papyrus. A few decades later, Mount Vesuvius in what is now Italy blew its top, burying Pompeii and the nearby city of Herculaneum, where the scroll was kept, in ash. When archaeologists uncovered the scroll and many of its companions in the 18th century, the fragile rolls were charred and mostly unreadable. “It’s a black cat at midnight situation,” says Greg Bearman, a retired physicist who has studied ancient scrolls.
Now, with the help of infrared imaging, researchers have finally been able to read writing hidden on the back of the charred scroll. The discovery may help reveal the secrets of other ancient documents.
Previous studies used different imaging techniques to decipher the dark ink on the front sides of the blackened papyri from Herculaneum. When researchers shone near-infrared light on the scrolls, hoping to increase the contrast, the carbonized paper reflected light in a way the carbon-based ink did not, revealing hidden letters. Other methods, such as x-ray scanning, helped scientists see inside some scrolls that remain tightly rolled.
The back of the scrolls, however, posed a different challenge. In the years after their discovery, many of the Herculaneum scrolls were damaged in failed attempts to unroll the scorched papyrus. When scholars successfully unrolled a scroll, they often glued it flat onto paperboard to prevent it from disintegrating into flakes. For those that had writing on the back, such as the papyrus containing Philodemus’s book, this preservation process meant the words on the back were lost to time, remembered only in a few pages of notes taken by draftsmen before the scroll was glued down.
To reveal the mysteries of the reverse side of the scroll, a team of classics scholars, papyrologists, and physicists decided to try a method, called short-wave infrared hyperspectral imaging, that had never been applied to papyri. Tested before on medieval palimpsests and illuminated manuscripts, the technique uses light with wavelengths between 1000 and 2500 nanometers—longer than visible wavelengths but short in terms of infrared—to expose what is undetectable to the human eye. The longer wavelengths of light are “very good for penetrating layers and reading inside a solid object,” says team leader Graziano Ranocchia, a classicist at the National Research Council in Rome.
Ranocchia and his team set up a mobile laboratory in the Italian national library in Naples, where many of the scrolls from Herculaneum are now stored. They began the process of imaging both sides of Philodemus’s scroll, which was littered with annotations and cramped notes in the margins. The researchers captured hundreds of images of fragments of the scroll illuminated with different wavelengths of light.
After some processing, the images revealed previously obscured text on the back and enhanced the readability of the words on the front, the researchers report today in Science Advances. Overall, the new imaging method added some 150 words to the current version of Philodemus’s manuscript, of which scholars have been able to decipher more than 8000 words so far.
The technique also allowed the researchers to correct some sections of Philodemus’s manuscript that had been wrongly interpreted. For instance, one Greek word that had previously been read as “charmed” or “bewitched” (as in, debate opponents of the philosopher Arcesilaus, the founder of the New Academy, were “bewitched” by their own arguments) turned out to say “enslaved” when viewed in starker contrast. Clarifications like this can change how scholars interpret Philodemus’s portrayals of famous thinkers.
The infrared imaging approach is a good way to “see” through the front side of the papyrus to the writing on the back, says Bearman, who has used spectral imaging techniques in the past to reveal the writing on documents such as the Dead Sea Scrolls, but who was not involved with the current study. Still, he says the researchers could improve the study by refining the data processing techniques.
With this technique, wrinkles or holes in the papyri could be mistaken for letters, a problem Ranocchia says could be fixed by using a higher resolution lens for their camera.
“I think it’s a good study, and I appreciate these guys for doing it,” says Brent Seales, a computer scientist at the University of Kentucky in Lexington who has imaged the Herculaneum scrolls in the past using different methods. Half the battle of testing techniques to read ancient papyri is being allowed to perform experiments on the fragile documents, he says, and Ranocchia’s team’s access to the archives at the national library was “a major accomplishment.”
Seales is eager to see Ranocchia’s methods applied to others of the nearly 2000 papyri from Herculaneum, even those without writing on the back. Opening a papyrus scroll can be a bit like “peeling an onion,” Seales says, in that layers are often stuck to each other and some parts flake off and stay stacked, even when the scroll is unrolled. The infrared technique, he says, could help scientists read what’s hidden between those layers.
Now that the team has established that the method works on papyri, Ranocchia hopes to tailor artificial intelligence software to reading obscured portions of ancient scrolls. “I would love to see them push the limits on what the infrared stuff can do,” Seales says.