Domus Transitoria

One of the main buildings is thought to be on the western side of the Oppian Hill under the Baths of Trajan.[3]

The brick walls of the palace were originally covered with marble at the bottom, while the upper parts were frescoed. A portico fronted the domus along the south side. Almost all of the columns, floors and marble walls were removed when Trajan built his baths (in 104 AD).[4]

The house was built around a big peristyle with porticos on three sides, while the fourth on the north consisted of a cryptoporticus which supported the rear embankment. At the centre, occupied now by a series of long barrel vaults to support the overlying Trajanic baths are the remains of a fountain; on the eastern part is a large nymphaeum that opens to the courtyard.

Fresco from the nymphaeum of the domus transitoria, 54–64 AD

An elaborate nympheum was unfortunately divided in two by a wall of Trajan. Surrounded by a portico of four columns it was equipped with a cascading fountain on the bottom, whose water was conveyed into a central basin. On the walls of the grotto was a mosaic of which only few traces remain within a frame of shells. The lower part of the walls were originally covered in marble.

The decoration of the vault, 10 m (33 ft) high, is preserved only in part where four corner medallions and a central octagon were inserted, the latter partly preserved representing the Polyphemus scene.

Five metres below Hadrian's Temple of Venus and Roma a sumptuous rotunda belonging to the palace was discovered in 1828, cut through by foundations of the Domus Aurea.[5] The elaborate domed room which interconnected two barrel-vaulted corridors was spectacular architecturally and had marble-lined pools and paving in multicoloured opus sectile, all still largely intact beneath the temple.[6]

Cryptoporticus of Nero, Palatine

The main part of the palace was probably on the Palatine Hill and a large and brilliantly decorated set of rooms has been located in the central part of the Palatine Hill under the Palace of Domitian. This site was excavated in 1721 when considerable damage was done during the excavations. The lower floors contained sunken gardens, two pavilions, a nymphaeum, and an art gallery. Beyond these rooms is a very large latrine, which has been wrongly thought to be the machinery chamber of a hydraulic lift, which would, it was supposed, have worked in a shaft over 35 m (115 ft) deep found not far off.[7]

In one of these rooms is a rich marble floor found under the oval fountain room of Domitian's Cenatio Iovis, and a rich nymphaeum with marble columns and bronze capitals. Today one corner of the nymphaeum has been rebuilt.

The cryptoporticus of Nero that connected the house with the nearby Domus Tiberiana was also part of the complex.

Marble and other parts salvaged from the ruins later became part of the Domus Aurea, Nero's main residence.

Painted ceilings with mythological scenes from the Domus Transitoria, the earliest examples of fourth-style painting, perhaps by the painter Fabullus, are displayed in the Palatine Museum.

In 2019 it was announced that this part of the palace will be accessible to the public for the first time in almost 70 years.[8]