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Beneath the soil in Cologne, Germany, lies a bibliophile's dream: an ancient Roman library that once held up to 20,000 scrolls, according to news reports.

Archaeologists discovered the epic structure in 2017 while they were excavating the grounds of a Protestant church to build a new community center. Considering Cologne is one of Germany's oldest cities, founded in A.D. 50, it's no surprise that it still has structures dating back to Roman times.

However, archaeologists didn't figure out that the structure was a library until they found mysterious holes in the walls, each measuring about 31 inches by 20 inches (80 by 50 centimeters), The Guardian reported.

The niches in the wall were likely "cupboards for the scrolls," Dirk Schmitz, an archaeologist at the Roman-Germanic Museum in Cologne, told The Guardian. "They are very particular to libraries — you can see the same ones in the library at Ephesus [in Turkey]." [Photos: Centuries of History Revealed Beneath Roman Ruins]

While it's anyone's guess as to how many scrolls the library once housed, it's fair to say the number would have been "quite huge — maybe 20,000," Schmitz said. He noted that the newfound library is slightly smaller than the Celsus Library in Ephesus, which was built in A.D. 117. Even so, its discovery is "really incredible — a spectacular find," Schmitz said.

"[It] is, at a minimum, the earliest library in Germany, and perhaps in the northwest Roman provinces," he said. "Perhaps there are a lot of Roman towns that have libraries, but they haven't been excavated. If we had just found the foundations, we wouldn't have known it was a library. It was because it had walls, with the niches, that we could tell."

The ancient Romans chose a good spot for the building, he noted.

"It is in the middle of Cologne, in the marketplace, or forum: the public space in the city center," Schmitz said. "It is built of very strong materials, and such buildings, because they are so huge, were public."

During its heyday, the library was probably two stories tall and measured about 65 feet by 30 feet (20 by 9 meters), and an extension was added later, Cologne historic preservation official Marcus Trier told Deutsche Welle (DW), a German news outlet. This extension was likely an alcove where a statue of Minerva, the Roman goddess counterpart to Greece's Athena, once stood, Schmitz told The Art Newspaper.

The ancient library's remains will be integrated into the new church community center, giving access to visitors and future archaeologists, DW reported.

Original article on Live Science.