In March 2000, the director of the British School at Rom, Professor Andrew Wallace-Hadrill, and the Soprintendenza and Comune di Roma, commissioned a geophysical survey over part of the Colle Oppio in the centre of Rome. The trial resistivity survey was partially successful in identifying potential archaeological structures associated with the Baths of Trajan. Results were more successful on the ground to the south and east areas of the park, where the depth of archaeological deposits is significantly less than across the more elevated areas of the park to the north. The lack of any recognisable archaeological features in the survey results in the north and north east of the park suggest that resistivity, certainly utilising a twin prove array, would not be an effective method of mapping sub-surface remains of the Trajanic baths across the entire archaeological park.

As a result of the archaeological discoveries made between 1998 and 1999 in the gallery beneath the southwestern corner of the Baths of Trajan on the Oppian Hill (that included among other finds the building with the fresco "Painted City" and the wall mosaic "Muse and Philosopher"), excavations and restorations are at present in progress in the Baths above the gallery, in order to render them waterproof. These excavations confirmed the presence of a large portico that ran along the inside of the entire western side of the Baths, exactly above the gallery. A few bases in travertine in the perimeter wall are all that remain of the portico's columns. There is no trace of the pavement above the extrados of the vault. The room formed by the southwestern exedra is commonly known as the "Great Library" because of the presence of two superimposed orders of niches. This room opened onto the portico, through a columned entranceway. A test excavation inside the exedra revealed three low concentric stairs on the inside perimeter, with ample remains of marble veneers. Another portico, of smaller dimensions and with smaller column bases, was discovered on the southern front of the Baths. Excavations are in progress on the western external part of the portico, where the stratigraphy of the Trajanic construction deposits is being investigated. (Giovanni Caruso-Rita Volpe)

Following the work undertaken between 1998-99, and the discoveries made in those years, funding was obtained under the L. 396/90 for Roma Capitale, which financed campaigns in 2003-2006 and 2007-2008. A museum is to be created in the gallery below the south-western exedra of Trajan’s baths (the so-called “cryptoporticus”), where in 1998 both the building with the large fresco of the “Painted City” and that with the wall mosaic of the “Muse and Philosopher” were discovered. With this in mind it was necessary to continue with the main objective, that is the guaranteeing of the best conditions for the conservation of the archaeological materials housed in this area. Prior to the excavation inside the gallery below the south-western exedra, the programme of works foresaw the waterproofing and consolidation of the vault prior to the removal of the late 18th century levels and the excavation of the stratigraphy above the vault itself. These interventions were to terminate with the re-laying of the preceding floor level. However, the situation uncovered by the excavations conditioned future excavation strategy. It was thus decided to proceed with a general renovation of the Trajanic level, waterproofing the vault’s extrados with a thick layer of opus signinum and reconstituting the line of the perimeter wall of the portico above the gallery. A trench dug inside the exedra revealed the presence of numerous remains both of the architectural structure and the facings, and it was decided to complete its excavation down to the original level. Excavation of the late 18th century dumps covering this entire area, relating to the “Fabbrica del Salnitro” (known as the Powder magazine) installed in this corner, revealed the presence of late antique dumps below, often cut by pits and cuniculi made during the Renaissance period in the search for treasure and building materials. The dumps relate to successive phases of the bath’s abandonment, datable to between the 6th-7th century A.D. Two isolated burials and scarce traces of occupation dated to the late antique period. The excavation of these dumps brought to light the original floor of the exedra in slabs of giallo antico and pavonazzetto marble (some of which still preserved); low steps ran along the edges of the walls, originally faced with white marble. The semicircular exedra (diameter circa 30 m), with two orders of rectangular niches, is traditionally identified with the library; the façade was articulated by four columns (of which the robber trenches were found) and by two semi-pilasters or semi-columns which stood against the two brick-faced ends of the exedra, delimiting the façade. The exedra faced onto a portico circa 10 metres wide which ran around the perimeter of the baths’ enclosure. The discovery of at least three travertine bases, which had supported the vertical elements of the portico (pillars or more probably columns), made it possible to reconstruct a colonnade with an intercolumniation of circa 3 metres looking out onto the green area surrounding the rooms dedicated to bathing. The portico stood exactly above the gallery (so-called cryptoporticus) which had been built to function as a foundation in the points where there were no pre-existing structures to use as a base for the terracing. Above the gallery, in correspondence with the building with the fresco, a passage which had opened in the vaulted roof led into the room below, part of the building’s original entrance. Its exploration revealed a large mosaic with a grape harvesting scene. The mosaic, previously only seen by video camera, was preserved on a side wall and must have been part of a larger surface decorated with mosaic, which with various pictures and registers decorated the entire vault. Thus the mosaic was part of the decorative scheme of the same large building, probably constructed in the Flavian period, in the last quarter of the 1st century A.D. Its façade was decorated by the fresco of the “Painted City”, at a height of almost fifteen metres from the ground, at the side of the grandiose archway, over ten metres wide, which constituted the main entrance. During 2009 both the vault and the mosaic itself were restored and consolidated.

The 2010 excavations investigated the room named of the “Vendemmia” after a large patch of preserved wall mosaic, and part of the mosaic decorating its vault. The mosaic was part of the decorative scheme of one large building, probably constructed in the Flavian period during the final quarter of the 1st century A.D. At a height of almost 15 m above the ground, the façade was decorated with the “Painted City” fresco, to the side of the grandiose arch that constituted the main entrance to the complex. Under various layers of collapse, at a depth of about 30 m a.s.l., the excavation exposed the mosaic surface of the vaulted ceiling, numerous building site surfaces, and dumps relating to Trajanic activity. Also in 2010, excavation began inside the gallery, in correspondence with the point where in 1998 a long transverse wall was found. Earlier in date, it presented a patch of wall mosaic showing a “Muse and Philosopher”.

In 2011, excavation continued at the centre of the gallery, also revealing various surfaces associated with the Trajanic construction site. In the room housing the Muse and Philosopher wall mosaic, the eastern sector, cut diagonally by the Trajanic walls, was excavated. Two of this room’s walls were exposed: one almost 16 m long, with new patches of figured mosaic; on the other wall, about 10 m long, also presented the remains of mosaic decoration. The decorative scheme presented a series of registers. Buildings in perfect perspective can be seen in the uppermost register with male and female figures inside them. At the centre is a man and as well as the Muse and Philosopher seen in 1998, a centaur, a dolphin, and numerous decorative elements can be recognised. The remains of a wall mosaic are also preserved on the south side of the room; at a lower level, the entrance to a nymphaeum, with the remains of a blue glass mosaic on the vault and a niche in the back wall with a hole for the _fistula_ , opened in this wall. The structure was almost completely buried.

In 2012, the excavation continued in the northernmost part of the room revealing most of the mosaic’s lower register. This was in a better state of preservation and a series of four female figures can be distinguished. Digging down from the wall’s crest a maximum depth of five meters was reached. According to the proposed reconstruction based on the presence of the nymphaeum, the wall was probably over 10 m high. The structure had two building phases: the first in large travertine blocks, with three openings; these were closed in a later phase when a brick-built storey was added, on whose surface the great wall mosaic was created.

Excavations continued in the so-called cryptoporticus, extending and deepening the trench on the side behind the wall with the mosaic. Here, the excavation of the layers of dumped material relating to Trajanic construction activity, further exposed the white plaster facing on the wall, which presented gaps and holes of various size and nature. At about 1.60 m below the crest of the wall, the plaster surface appeared a groove, underneath which Latin graffiti were visible. Inside the gallery, the excavation of the Trajanic beaten floor surfaces inside the room with the wall mosaic continued, exposing new parts of the mosaic composition on the wall.