The Library of Ancient Philippopolis is one of the public buildings forming the northern part of the Forum, located to the West of the Odeon. The building plan is rectangular in shape with approximate dimensions of 15 x 20 meters.

The formation of the walls of the library interior is really interesting. The Roman brick masonry allowed the formation of niches in the inner side of the building. Presumably, in those niches were placed wooden cabinets for storing scrolls. The floor of the Library was paved with marble slabs.

It is curious how a better air circulation system in the area of ​​the Library was constructed. It is well known that moisture distorts the structure of written texts, which at that time were performed mostly on papyrus. In the brick walls surrounding the library, vertical clay pipes were embedded, which ended in a channel leading the water away into the drainage system of the Forum.