A thousand-year campaign by Christians to stop musicians from playing the "Devil's Interval" has been a complete failure, the BBC reports today.
The tritone is a spooky-sounding musical interval that medieval Catholics believed was actually evil. Monks weren't allowed to sing the notes and composers couldn't use them.
As the church began to lose its power during the Reformation and the Enlightenment, composers ignored religious rules and used the Diabolus in Musica with abandon.
The dramatic tritone can be heard everywhere today, from the first notes of "The Simpsons" theme to the opening of "Purple Haze," Wagner operas to the orchestration for almost any suspense movie. Black Sabbath got its signature satanic sound by plodding along on tritones -- a hard-rock trademark even "Christian" metal bands religiously copy.
"In the Middle Ages when people were ignorant and scared, when they heard something like that and felt that reaction in their body they thought, 'Uh oh, here come the Devil,'" says rock producer Bob Ezrin.
Some musical historians say the tritone just didn't work in medieval music and the "Devil's Interval" was just a figure of speech used to describe something difficult or wrong.
But in the Middle Ages -- just like in the United States today -- most people literally believed that everything wrong or weird is the work of an actual all-powerful sadistic Devil deliberately created by God just to pointlessly torture humanity.
The only explanation for something being wrong was that it was demonic. The Devil caused everything from bad luck to mental illness, failed crops to birthmarks.
But even back in the Dark Ages, there were forces working against the church's crusade against the Devil's Interval.
It was revealed in February that the ceiling of the famous Rossyln Chapel in Scotland, built in the mid-1400s, is encoded with the Devil's Chord.
William Sinclair, the designer of the bizarre chapel, supposedly hated the Roman church because it brutally suppressed the Knights Templar. Popular theories say Sinclair was a member of that ancient order of warriors.