Foundations of learning: uncovering a Roman library beneath the streets of Cologne. From the article:

Archaeologists had expected many things on this site, only certainly not a library, which now is considered the oldest on German soil. It was built between 150 and 200 CE on the southwest corner of the forum. Marcus Trier, Director of the Römisch-Germanischen Museum and head of the Cologne antiquities council, said, “according to our knowledge this is the first Roman library for which we have evidence.”…

A room has been uncovered, 20 meters long and nine meters wide that still had an apse. Two small “carefully polished” pieces of tile have been recovered, but above all the foundation walls. These were built from a mixture of chalk and trachyte [a volcanic rock], Roman “opus caementicium” or cement work. Its “category of durability,” according to laboratory tests, corresponds to that of high-quality cement of our times. Christoph Meyer, foreman of the site, believes that this “C 25/30” quality would suffice for a modern single-family house. Meyer speaks with great respect about the work of his ancient colleagues: “We can still see the impressions of the scaffolding that they used. Fundamentally the Romans did not build very differently from we today.”…

The first speculation focused on a college or a type of gathering hall. Then the key of the building came to light: niches in the inner walls, which were too small for statues. Comparisons with other ancient buildings — Ephesus, Pergamon, Alexandria, or Rome — indicated that in these niches, about 80 centimeters wide, lay chests or containers for parchment or papyrus rolls. The rolls was affixed with labels, said [the archaeologist Dirk] Schmitz, in order to indicate which writings were contained there. There were most likely ladders in order to reach the higher shelves; perhaps there was also a wooden balcony.