The Horti of Agrippina, the large villa built by the mother of Emperor Caligula, extend on the south side of Via Cornelia, the road that at that time linked the Neronian Bridge to the Vatican mountains. The exact boundaries of the vast imperial possession are still not well known, but from the ruins of the buildings found out in the area and from the information provided by ancient sources, we know that they must extend between the northern slopes of the Gianocolo, the right bank of the Tiber river and the Borgo plain, occupied in ancient times by the Horti of Domizia. It is believed that Agrippina Maggiore may have received these gardens as inheritance from her husband Germanico or from her father Agrippa, Augusto¿s son in law. On Agrippina¿s death in 33 A.D. her son Galigula owned the Horti. Among the buildings that made up the vast complex, sources indicate a terrace and a porticus facing the shore of the river; a residential building located between the Gianicolo and Vatican, indicated in the medieval texts as Palatium Neronis and the big Vatican circus (circus Cai et Neronis) that extended into the area where now stands the basilica of S. Peter. To this last complex, that was the site of the sacrifice of the early Christian martyrs after the fire in 64 AD, belonged the obelisk that now is placed at the center of the square. Numerous remains of buildings have been found out in the course of the time, throughout the area that once was occupied by the villa. Among the most important ones, we remember the buildings present under the S. Spirit Hospital and the large domus recently discouvered by the Gianicolense tunnel at the southern end of the Horti. The visible complex under the hospital consists of brickwork and reticulated structures dated between the I and II century AD. Among them there is a large exedra opening to the River. In the past, a marble basin with carved marine scenes was found in this area, attributable to the first century AD. The recent excavations at the eastern entrance of the tunnel, brought to light a domus belonging to the Imperial age (perhaps attributable to the Horti) whose interiors are decorated with frescoes containing architectural motifs, flowers and animals (birds). Some rooms of the house were used as a deposit of numerous marble elements, during a renovation or a change of use of the building. These are pilasters, capitals and bases, in various types of marbles, which were probably part of the decoration of a ninfeo. From the type of fresco decorations, building techniques used and from some "bolli" bricks found during the excavation, we can assign the complex to the II century AD, that is, a period when the villa should have reached its maximum extension. F. A.