Something unusual happened at the Pembroke College Chapel in Cambridge, England, over the weekend: A trio of musicians performed songs that hadn't been heard in over 1,000 years. But playing the music, which came from the Roman philosopher Boethius’ influential work The Consolation of Philosophy, was not just a matter of just reading its notation. Rather, getting Boethius' work to the public's ear involved solving a decades-old library theft, not to mention the arduous process of deciphering the symbols representing musical notation in the Middle Ages.

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The theft occurred in the 1840s, when a German scholar visiting the university surreptitiously snipped a page from an 11th-century manuscript known as the “Cambridge Songs,” according to a press release from Cambridge. That the scholar took a page of music notation and lyrics from Boethius home with him remained a mystery until 1982, when a researcher from Liverpool University named Margaret Gibson visited a library in Frankfurt. When Gibson asked to see any materials by Boethius, she was stunned to be handed the missing page from the Cambridge collection.

As it turned out, the missing page was the heart of the song collection. “Without this extraordinary piece of luck, it would have been much, much harder to reconstruct the songs,” says Sam Barrett, a specialist in medieval music at Cambridge who led the project to revive the songs. “The notations on this single leaf allow us to achieve a critical mass that may not have been possible without it.”

The Consolation of Philosophy was written at a time when music notation employed a much looser method than what is used today. While medieval “neumes” present a melodic direction and some details on vocal delivery, they do not dictate a note-by-note roadmap for a piece of music. Many of the details of musical delivery were passed along through an aural tradition, which died out centuries ago. Now, scholars can only make educated guesses as to what the music sounded like.

Barrett was able to piece together about 80 to 90 percent of the melody of the Boethius songs, but enlisted Benjamin Bagby of the early music group Sequentia to help work through the rest. “Ben tries out various possibilities and I react to them—and vice versa,” Barrett says in the press release. “When I see him working through the options that an 11th century person had, it’s genuinely sensational; at times you just think ‘that’s it!’ He brings the human side to the intellectual puzzle I was trying to solve during years of continual frustration.”

According to Mark Miller at Ancient Origins, The Consolation of Philosophy is considered to be the last great work of the Classical era, and was admired and translated by Alfred the Great, Chaucer and Queen Elizabeth I. It was written while Boethius, once a prominent senator and consul of Rome, was awaiting execution for treason against Theodric the Great, one of the first Ostrogoth kings of Italy, the tribe that took over after the fall of Rome. The book takes the form of a conversation between Boethius and the spirit of Philosophy. It’s unlikely that he ever intended for the work to be set to music, but it was common in the early medieval period for classical poetry and other works to be reworked into songs.

For Barrett, hearing the music performed is the culmination of years of research. “There have been times while I’ve been working on this that I have thought I’m in the 11th century, when the music has been so close it was almost touchable,” he says in a statement. “And it’s those moments that make the last 20 years of work so worthwhile.”