When a Norwegian librarian posted to Reddit a map from a 19th century atlas he had recently found on the shelves while working, he didn’t expect to find out he had made a discovery that sounded like the plot to an episode of a TNT series or a National Treasure reboot (think International Treasure: Norway or the Highway).

Reddit user PisseGuri82, who works at the National Library of Norway in Oslo, unearthed a rare copy of the 1803 Cedid Atlas Tercumesi, “the first Muslim-published world atlas based on European geographic knowledge and cartographic methods,” according to information from the US Library of Congress about its copy of the reference book.

Only 50 copies of the atlas from the Ottoman Empire were printed, but an unknown number of those were destroyed in a publishing house fire before being released, according to PisseGuri82, whose name is Anders Kvernberg. Until Kvernberg’s discovery, only 14 copies were known to exist.

The librarian—and archivists everywhere—have redditors to thank, however, for helping identify Kvernberg’s find and reveal its significance.

“I found this (uncatalogued) copy at the library where I work, and casually scanned one of the nice maps for my [Map Porn community] post here,” Kvernberg wrote in the comments thread of a Map Porn community post by another Reddit user spotlighting a different copy of the Cedid Atlas. “It’s in slightly rough condition, containing 22 of the 24 maps as well as the 80-page geographic treatise preceding the map part. So … It appears we are the 12th library in the world to hold a copy of this atlas. Now I think I have to go talk to my boss …”

Kvernberg had found the atlas about a month ago on a library shelf, but he didn’t think he had discovered anything special.

“It looked like it was untouched for years, but then again a lot of our stuff is,” he wrote in the comments thread of a Best Of community post about his finding. “Of about 150,000 maps and atlases, I would guess a couple of thousand are used during a year. … So I scanned some of the maps, stitched them rather poorly, and made [a Reddit] post, just for fun. As you can see from my comments, I was not aware of what atlas this was or its history at the time.”

It wasn’t until a few weeks later that Reddit user unord posted a scan of the Library of Congress’ copy of the Cedid Atlas to the Map Porn community, and redditor naharin made Kvernberg aware in that post’s comments thread that he might have an original copy of the atlas on his hands. Once the librarian realized this possibility, he alerted his supervisors and began looking into the atlas’ history, as well as the history of the particular copy he had found.

In another comment, Kvernberg says he believes he knows who the copy’s previous owner was and when the copy came into the library’s possession. And thanks to his research, he’s even developed a theory on how the previous owner got the atlas.

While the events of the past days have been far from routine, this type of thing is a bit familiar for Kvernberg, who experienced something similar fairly recently.

“Of course this is very exciting,” he wrote. “This is the kind of thing that only happens … well, every odd year. It’s been a couple of years since we last found a rare map: the fourth known complete copy of the 1719 Ramus map of Norway. That was actually worth more, both money-wise and in terms of relevance to our collections. Still, one of the rarest atlases in the world is no small find!”

For now, Kvernberg has posted another scan from his discovery—a map featuring Europe—and revealed the library’s plans for its copy of the Cedid Atlas.