Baths of Caracalla
Rectangular halls connected to the hemicycle have been suggested to be libraries because of their similar set-up to those in the Baths of Caracalla. Historians, to support this theory, have demonstrated that these halls with their niches could properly house scrolls and/or codices. (The author of the Life of Probus mentions that part of the Bibliotheca Ulpia, was located in the Forum of Trajan, and part within the Baths of Trajan, although he later contradicts that statement when referring to the "Bibliotheca Ulpia)." The presence of similar spaces in the Baths of Caracalla and the Baths of Trajan therefore makes it not unreasonable to assume that the baths of Diocletian contained a library.