It has stumped code breakers, language experts, and mathematicians. The mysterious medieval book known as the Voynich Manuscript was written in a script that no one can understand and has drawings of plants that don't exist.
But the latest study of the 15th-century text known as "the world's most mysterious manuscript" concludes it may contain "a genuine message."
Statistical analysis of the script by researchers including a University of Manchester physicist shows its overarching semantic structures reflect those that appear in real languages. That suggests it is not a hoax as some have said.
Named after book collector Wilfrid Voynich, who purchased it in 1912, the manuscript dates to the early 1400s and consists of about 240 pages of vellum.
While it looks like a typical medieval codex, it's illustrated with pictures of herb and plant species, none of which can be positively identified, as well as bizarre pipe-like structures, cosmic maps or diagrams, astrological imagery, and naked bathing women.
In 1969, it was donated to Yale University's Beinecke Rare Book and Manuscript Library and cataloged as a "Cipher Manuscript." No one, not even wartime code breakers, has been able to tease any meaning out of its strange "Voynichese" writing, and no other example of this writing has ever been discovered.
With its bizarre word repetitions, it has been variously judged to be forgery, a constructed nonsense language, or an encrypted book of knowledge that is meaningful in some European tongue.
The new study in Plos One by theoretical physicist Marcelo Montemurro and Argentina's Damian Zanette brings more computerized statistical analysis techniques to bear on the text.
In looking at the frequency and patterns of various words and their distribution over the entire book, as well as their relationship to other words, the researchers focused on a "statistical signature" suggesting it's not just gibberish.
"We show that the Voynich manuscript presents a complex organization in the distribution of words that is compatible with those found in real language sequences," they write.
"We are also able to extract some of the most significant semantic word-networks in the text. These results together with some previously known statistical features of the Voynich manuscript, give support to the presence of a genuine message inside the book."
Previous research has also shown that Voynichese is similar to real languages. What the words may mean, however, and whether they represent an encoded known language or a completely made-up one, is still up for debate.
Some enthusiasts have constructed their own linguistically complex nonsense languages to prove that the Voynich Manuscript is something that a mischievous 15th-century scribe could have pulled off.
"After this study, any new support for the hoax hypothesis should address the emergence of this sophisticated structure explicitly," Montemurro told BBC News. "So far, this has not been done."
"There must be a story behind it, which we may never know."