The remains of the oldest public library in Germany, a building erected almost two millennia ago that may have housed up to 20,000 scrolls, have been discovered in the middle of Cologne.

The walls were first uncovered in 2017, during an excavation on the grounds of a Protestant church in the centre of the city. Archaeologists knew they were of Roman origins, with Cologne being one of Germany’s oldest cities, founded by the Romans in 50 AD under the name Colonia. But the discovery of niches in the walls, measuring approximately 80cm by 50cm, was, initially, mystifying.

“It took us some time to match up the parallels – we could see the niches were too small to bear statues inside. But what they are are kind of cupboards for the scrolls,” said Dr Dirk Schmitz from the Roman-Germanic Museum of Cologne. “They are very particular to libraries – you can see the same ones in the library at Ephesus.”

It is not clear how many scrolls the library would have held, but it would have been “quite huge – maybe 20,000”, said Schmitz. The building would have been slightly smaller than the famed library at Ephesus, which was built in 117 AD. He described the discovery as “really incredible – a spectacular find”.

“It dates from the middle of the second century and is at a minimum the earliest library in Germany, and perhaps in the north-west 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 building would have been used as a public library, Schmitz said. “It is in the middle of Cologne, in the marketplace, or forum: the public space in the city centre. It is built of very strong materials, and such buildings, because they are so huge, were public,” he said.

The walls will be preserved, with the three niches to be viewable by the public in the cellar of the Protestant church community centre, which is currently being built.