Titus Flavius Severianus Neon, a member of one of the most important families of Sagalassos built this library in ca.120 AD, in honour of his deceased father. In many ways, it resembles the Library of Celsus at Ephesus (114 -117 AD).
Today only the podium of the rear wall belongs to the original building phase. The niches in the podium held small statues and a series of inscriptions were placed on a row of slabs above them. In the inscriptions, Neon and some members of his family are honoured by the city council (Boulè) and the assembly (Dèmos). The back wall, made of solid brick, belongs to the second building phase of the library (200 AD). During this renovation due to structural problems, the interior of the Library was made narrower. The side walls date back from this building phase.
The mosaic floor dates from a second renovation phase. dating to the reign of Emperor Julian the Apostate (361-363 AD). The middle panel of the mosaic depicted a scene from the Trojan War, showing Achilles saying farewell to his mother Thetis before leaving to join the war. Towards the end of the fourth century the mosaic panel were destroyed by the Christians, since they were symbols of pagan culture. The large cracks on the floor are the result of the earthquake of the 610s AD.