The Baths of Diocletian are one of the four seats of the National Roman Museum, the others being Palazzo Massimo, Palazzo Altemps and Crypta Balbi. Today, the bath is taken up mainly by the Museum of Epigraphy which collects and conserves written texts on various themes from the eighth century B.C. to the fourth century A.D.. The magnificent structure of the bath, the largest in Ancient Rome, was built between the years 298 and 306 A.D. As well as holding the traditional pools of water at various temperatures (calidarium, frigidarium and tepidarium), the bath also included a central hall, an open-air swimming pool and many other rooms which were put to various uses. Today, part of the perimeter of the bath is occupied by the Church of Saint Mary of the Angels. Indeed, in 1561 Pope Pius IV decided to change the bath into a basilica with an annexed convent, and commissioned Michelangelo to bring this to fruition. In 1889 the baths became a seat of the National Museum of Ancient Rome and diverse archaeological collections were kept there. The large cloister holds about 400 sculptures displaying the whole range of artistic styles found in Ancient Rome. The galleries of the cloister are dedicated to a permanent exhibition on pre-historic populations and the development of their cultures in Latium in the late Bronze Age and iron age (twelfth to seventh centuries B.C.), with particular reference to Rome. The epigraphic section was created in the early nineteenth century and today is completely restored. This part displays the birth and diffusion of the Latin language through various written documents such as the 'memorial stone of the Forum', 'the limestone crown from Palestrina', 'the defixiones', and 'the tituli', as well as texts related to associations and a group of texts which narrate the development of Roman society throughout the period.
The multimedia room hosts a virtual reality installation, which makes it possible to explore the reconstructions of monuments and sites located along the ancient Via Flaminia, including the Villa of Livia at Prima Porta. The octagonal room, that became a Planetarium in 1928, has an intact marvelous cupola and today hosts sculptures of the baths. Among the most important of these is the famous Aphrodite of Sirene, a replica made in Hadrian’s age of a piece by Praxiteles . The halls of the Renaissance period, in which oil used to be stored, are now utilized, after recent restoration, for conferences and exhibitions.