On the left of the entrance are the remains of the ORATORIO OF S. FELICITA, a Christian church of the sixth century. The rooms on the left of the PASSAGE, substructions formed by Hadrian, are supposed to have been used as private habitations in the middle ages. On one of the piers are two snakes (_see below_). At the end of this Passage a part of the pavement of the HOUSE OF NERO can be seen. LONG CORRIDOR, penetrated into by Raphael and Giovanni da Udine, who copied the frescoes for the Vatican. On the vault are some beautiful arabesque paintings of flowers, birds, and animals; and on the walls two snakes, with a basin placed between them. Above them is an inscription, now almost obliterated, telling us that it was the notice equal to our "Commit no nuisance." DVODECIm DEOS IIT DEANAm ET IOVEM OPTVMVm MAXIMVm HABEAT IRATOS QUISQUIS HIC MIXERIT AUT CACARIT. _Retracing our steps_ down the corridor, and crossing some chambers, we come to the TRICLINIARIUM, or summer banqueting room, with the winter rooms on each side, having a southern aspect. At the end of this room there was originally a garden; and in the basin of the fountain was the porphyry vase now in the circular hall of the Vatican Museum. Beyond this is the CAVÆDIUM, an open court or garden, from which the surrounding apartments received their light. It was surrounded on three sides with columns, and in the centre was a fountain: it was subsequently occupied by the substruction arches of the baths. Adjoining is the CORRIDOR OF RHEA SYLVIA, so called from the fresco representing the conception of Romulus and Remus. In another room is a representation of Venus and the Doves. THE BATHS OF HADRIAN. On the Plan, the dark lines show the remains of Nero's Palace, which was nearly destroyed by the Flavian emperors. The remains left were used by Hadrian for the underground part of his thermæ; and by building walls over the courts and gardens he formed a large platform. The light lines show his work. The circular wall in front supported the seats for the stadium attached to the baths above. Remains of some of the large halls of the baths can be seen in the vineyards above the House of Nero. Some remains of these baths exist under the Church of S. Martino. These baths are generally ascribed to Titus; but the construction, _opus reticulatum_, within bands of brick, shows that they are of the time of Hadrian. _Turn to the left on coming out. A short way up the road, on the right, is the entrance to the_ CHURCH OF S. CLEMENT, belonging to the Irish Dominicans, of which the late Father Mullooly was prior, to whose instrumentality we are indebted for the discovery of the ancient church, and the Temple of Mithras beneath it, under the present edifice. On some occasions (November 23rd, February 2nd, and the second Monday in Lent) they are illuminated. Father Mullooly has written a book on his discoveries; it can be purchased of the sacristan, and will be found very interesting.