It was the most impressive spa complex in Rome and of the Roman world, it occupied a huge area between the current Via Torino, Via Volturno, Piazza dei Cinquecento and Via XX Settembre.
It was made up of an extensive central area which held the real bathing facility, which symmetrically arranged according to the lower axis that included the swimming pool, the frigidarium, the tepidarium and of a series of different kinds of rooms, such as a semicircular exedra with steps corresponding to the current Piazza della Repubblica ex Piazza Esedra, on whose sides there were the two rectangular halls used as libraries; it presented a very rich decorative display including sculptures, reliefs, marble baths, valuable objects, etc. In 1561 a basilica inside the complex was dedicated to the Madonna of the Angels with an attached convent, designed by Michelangelo; with the passing of time the rooms of the baths underwent numerous interventions that altered their original function.
The interventions culminated in the urban transformations associated with the declaration of Rome as the capital of Italy which involved further modifications to the complex, in particular the construction of Via Cernaia that cuts the structure in half and the construction of new buildings in the surrounding area.
It has been the headquarters of the section of Roman antiquities since 1889.
The cloister of the Carthusian Monastery of S. Maria degli Angeli, whose design is attributed to Michelangelo, has been completely restored after a painstaking intervention that has made it possible to emphasise its typology and the original finishing touches.
The organisation of the art works which occupy the four ambulatories has also been redefined, they are placed on bases that allow an optimum enjoyment of the sculptures.
The finds, which come mostly from chance discoveries in different parts of the urban and the suburban areas, are placed according to conventional topographic criterion: inside the Servian Walls, the consular roads, the Tiber, etc.