Musicologists from the University of Cambridge, who are apparently bored with Beyonce's Lemonade already, used ancient manuscripts to recreate a song from the 11th century. According to Gizmodo, the medieval tune, called "Songs of Consolation," is a musical retelling of The Consolation of Philosophy, a work by Roman philosopher Boethius. Listen to an excerpt below.
If you took the Lord of the Rings soundtrack, put it in a time machine with Sufjan Stevens, sent the time machine back to the Middle Ages, had a peasant woman mate with Sufjan Stevens, made their offspring learn the harp and listen to the Lord of the Rings soundtrack, and then recorded the results in a cathedral, you might get something like this.
No promises though, if you were thinking about trying that out.
Sam Barrett, a Cambridge musicologist, has spent two decades putting this piece together from neumes, which Gizmodo describes as "symbols that represented musical notation back in the Middle Ages, and a precursor to modern notation."
Barrett elaborates on neumes and the difficulties of reconstructing the song accurately:
Neumes indicate melodic direction and details of vocal delivery without specifying every pitch and this poses a major problem. The traces of lost song repertoires survive, but not the aural memory that once supported them. We know the contours of the melodies and many details about how they were sung, but not the precise pitches that made up the tunes.
Here's another Sequentia tune, this one sounding exactly like the time machine scenario above but replace Sufjan Stevens with the Fleet Foxes and put them in an even more reverberant location, like a middle school gymnasium.