Cryptology technology: shedding light on ancient secrets

When Alan Turing developed the machine that helped to crack the Enigma code, his aim was to understand messages that the Nazis wanted to keep secret. When ancient writing expert Roger Tomlin came across wooden tablets found recently at an excavation site in central London, he knew the words – now mere scratches on wood but originally marked in beeswax with a metal stylus almost 2,000 years ago – were not meant to be a secret. However, it took him a year to decipher them.

The tablets are the oldest handwritten documents found in the UK, detailing financial transactions and events in early London, starting a few years after the Roman invasion of Britain; they even mention events related to the revolt of Queen Boudica of the Celtic Iceni tribe in what is now East Anglia, who stood up against the occupying forces of the Roman Empire.

The treasure trove of documents was discovered under a 1950s office block, when it was being cleared to make space for the new European headquarters of financial news provider Bloomberg.

Everyday life may have seemed mundane to Junius the Cooper, Julius Classicus, and other inhabitants of the London of their time. However, for Tomlin, decrypting their writing was the equivalent of hopping into a time machine and watching an unknown ancient world unfold before his eyes. “Often, this is evidence which we were not intended to have – such as ‘literary’ historians wrote for us – and thus it is still more valuable,” he says. “And it is exciting to read something which has not been read for so long.”

Documents that have survived 1,700 years and more are relatively rare, and decrypting them – if it’s possible at all – is never easy.

For centuries, researchers had to decipher ancient documents by their own efforts, usually with the help of ‘frequency analysis’ – cataloguing how often each symbol appeared, which allowed them to make an educated guess as to the meaning of each. Today scientists are turning to technology for help.

In general, to decrypt ancient papyri with ink-written texts, researchers use infrared photography and multispectral imaging, with image data captured at specific frequencies across the electromagnetic spectrum. For decoding of wooden (incised) tablets and lead tablets, they also use new photographical devices that take a series of images.

Tomlin claims that he uses digital technology “less than some scholars in the field”. To uncover the London tablets’ secrets, Tomlin first photographed them with multi-directional light, then used Adobe Photoshop to make ‘tracings’ on drafting film in ink, referring all the time to the original object under a microscope beside him. Photoshop helps him to work from several images, because an incised text cannot be fully recorded with lighting from a single direction.

“There has been research on ways to distinguish electronically between ‘noise’, casual damage, and deliberate strokes in incised texts,” he says. “This is undoubtedly the way forward, but the problem hasn’t been solved yet.”

His technique is “as much an art form as it is a science”, Tomlin adds, because he has to account for different handwriting styles, errors and incomplete texts, with some writing even more difficult to decipher when the stylus had only partially penetrated the wax to mark each tablet’s surface. 

Tomlin also works with lead tablets – as does Jürgen Blänsdorf of the Johannes Gutenberg University Mainz. The most recent ancient documents Blänsdorf worked with were 34 inscriptions written on small lead sheets and beakers that were found in the sacred well of the early Roman nymph called Anna Perenna at Rome. The inscriptions can be dated from about the middle of the third century AD up to the beginning of the fifth – and the contents are curses called down on private persons because of theft, bribery, rivalry, jealousy, and so on. “The practice of the authors of the curses is to invoke demons like the nymphs of the well or those of the netherworld or oriental gods like Abraxas to punish the culprits,” explains Blänsdorf.

Like Tomlin, Blänsdorf finds the most useful instrument for the decryption of non-standardised handwriting is the binocular microscope. It allows him to detect the engraved letters from different directions and to take high-resolution photographs. “The lines of the inscriptions are mostly very faint and blurred by oxidation and encrustation,” he says. “The next step is to design everything on paper, marking both sides of the lines in order to show which line was engraved first, which one crossed it afterwards.”

The most difficult process, says Blänsdorf, is finding out the special forms of the alphabet used, then detecting whole words and phrases, and finally understanding the whole text – sometimes doing it several times in a row. “Decryption is a recursive process,” he says.

On the upside, he does not have to decipher the multiple layers of texts that may be found on wooden tablets, because their beeswax surfaces could be smoothed for re-use, so they often have scratches from many different texts and writers.

Other researchers, such as Alan Bowman, the director for the Centre for the Study of Ancient Documents at Oxford University, have begun to use RTI (reflectance transformation imaging), which produces video-like imaging of an incised text. “Essentially, we capture a number of images with the writing surface lit from different angles, then use software which synthesises the images – up to 75 of them – and allows the viewer to simulate the movement of light around the surface,” explains Bowman. During his career, he has worked on the ancient wooden tablets found in the Netherlands and Vindolanda, near Hadrian’s Wall, as well as a papyrus discovered at a site in northern France, and some stone inscriptions from Egypt.

Using technologies like multispectral imaging has been a game-changer, says Bowman. “Forty years ago, we used standard cameras with infrared film, or techniques such as making papier-mâché impressions of writing on stone, French chalk shaken over wooden surfaces with incisions to bring out the writing more clearly, or even reading ink texts on pottery immersed in water.” Today, only papier-mache impressions – also called ‘squeezes’ – are still used, to record incised texts on stone; some ‘squeezes’ have survived since the 19th century.

The use of technology doesn’t stop there. In 1998, Uppsala university linguist Christiane Schaefer attempted to decipher a stubborn 260-year-old handwritten manuscript that had been found in an academic archive in the former East Germany. But its 105 befuddling pages of odd symbols and Roman letters proved too engimatic, and Schaefer resigned herself to shelving it. However, in 2011, at a University of Southern California conference, she listened to a presentation by computer scientist Kevin Knight about machine translation – in which algorithms translate one language into another. She sent Knight her manuscript and, within just a few weeks, his researchers had cracked the first few pages. Or rather, their technology had. Knight used a statistics-based translation method to decode what is now known as the Copiale Cipher, a description of a ritual from a secret 18th-century society called “high enlightened (Hocherleuchtete) oculist order” of Wolfenbüttel, or Oculists. The society used sight as a metaphor for knowledge.

The entire document had only two non-coded inscriptions, “Philipp 1866” and “Copiales 3”. At first, the researchers thought the information was contained only in the Roman letters instead of the symbols. But that path led nowhere. Finally, they assumed, correctly, that the Roman characters were so-called ‘nulls’, put in to mislead the code breaker, and represented spaces, whereas actual words were made up of the mysterious symbols. As the text came from Germany, the scientists guessed that the language was probably German, and reverted to language-translation techniques like expected word frequency to find the letters corresponding to each symbol.

Sometimes code breakers are not that lucky. With or without machines, some ancient inscriptions can remain an enigma. At other times, researchers think they’ve got a translation but get it wrong. “The imaging process produces better visualisation, but correct decipherment and interpretation of the text depends on the knowledge and skill of the expert reader, who might still get it wholly or partly wrong, depending on how skilled he or she is,” says Bowman.

Tomlin agrees. “We can never be sure that a decipherment is fully accurate, although if it makes sense internally and fits what we know from other sources, that gives confidence,” he says. He remembers once deciphering a lead tablet from Bath that had been read many years before as a Christian letter warning a woman against the arrival of a heretic preacher in that city. The tablet was since lost, but a photograph was still available, and Tomlin was able to read it the other way up as a curse against theft.

“This was easier for me than for the original student of it, since I knew Roman handwriting better than he did, and many such lead tablets from Bath had been discovered since, so I knew what to expect,” says Tomlin. “But this too points a warning: it is said that archaeologists who set out to find something – end up by finding it.”

Some cases of misinterpretation are spectacular, adds Blänsdorf. The first decryption of a lead tablet found at Gellep on the border of the Rhine contained a fatal error caused by the special form of only one letter, the E in late cursive writing. The text seemed to mean an invocation of a demon to escort a group of Roman legionaries tormented by a cruel officer from the border of the Rhine back to their home on the Nile. But the text suffered from several unusual words, names and phrases. “Then I found it meant a curse of some private persons who should be scorned by the gods because of some crime and that nothing else (nilum!) could be added to the curse,” he says. “So every word had its place and its usual meaning.”