Function and meaning
It was a closed garden that served to give access to several surrounding buildings.
On the north side two narrow corridors on either side of the Nymphaeum CB3 led to the Upper Terrace of the Libraries, and some doors open towards the Latin Library and the Greek Library.
On the east side there were two other entrances towards the Hospitalia and from there to the Imperial Triclinium.
On the south side there is the entrance to the Cryptoporticus with Mosaic Vault. Two symmetrical stairs, built inside the retaining wall, went up to the Imperial Palace, together with a third stair which is still in use today.
Finally, on the west side there is an access to the Baths with Heliocaminus and a stair that descends to the Maritime Theater, which is on a lower level.
The opus sectile pavements prove that the building belonged to the noble quarters of the Villa reserved for the emperor.
See: Marina De Franceschini, Villa Adriana. Mosaici, pavimenti, edifici, 1991. Cortile delle Biblioteche: pp. 93-97 e 391-396.