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Baths of Diocletian

The Baths of Diocletian were the largest thermae ever built in Rome. The complex, constructed in the early third century, could accommodate an estimated three thousand people.

Parts of the bath complex have survived thanks to their incorporation into newer structures. What remains today of these baths are a testimony to its ancient grandeur, which extended 13 hectares.

The Thermae

The baths were built between 298 and 306 AD by Maxentius who had the complex named Thermae Diocletiani, after Diocletian, and was continued after his and Diocletian’s abdication under Constantius, father of Constantine.

In the early 5th century, the baths were restored.[The baths remained in use until the siege of Rome in 537 when the Ostrogothic king Vitiges cut off the aqueducts.

The Bathing Ritual

For Romans, bathing was a social event and the huge bathing complexes reflected their importance in Roman society. A visit to a bath complex like that of Diocletian started in the apodyterium, where visitors stored their clothes. They then progressed to the frigidarium (the cold water), the tepidarium (warm water) and the caldarium (hot water). Some visitor went to the sudatorium (sauna) before going to the caldarium. Men and women bathed separately.

But a visit to the baths was more than just about getting clean and relaxed. People came here to socialize, discuss politics, recount daily events and gossip. It was also a fitness and leisure center: there was a swimming pool, a massage room and complexes like that of the Baths of Diocletian boasted amenities such as sporting facilities, libraries and meeting halls.

The Bathing Complex

The Baths of Diocletian measured 356 meters long and 316 meters wide (about 1200 x 1000 ft) and were the largest of the approximately nine hundred bath houses in Rome. The enclosed complex was structured similarly to the Baths of Trajan and Baths of Caracalla, with a central axis around which the actual baths were located. The water supply was provided by the Aqua Marcia, an aqueduct that had long served the city of Rome since the early 2nd century. Water was led to a large water basin  situated near the current Termini train station, which derived its name from the thermae.

The Baths Today

After invading Goths destroyed the aqueduct in 537 AD, the baths were soon reduced to ruins. Later the remains of the complex had to make way for the expanding city, but parts have been preserved as they were incorporated into new buildings such as the pantheon-esque San Bernardo alle Terme church and the Aula Ottagona, an octagonal hall. Another church, the Santa Maria degli Angeli, also reused a section of the ancient bath complex.

In the 1560s, Pope Pius IV ordered the building of a basilica in some of the remains. To this was attached a Carthusian charter house. Michelangelo was commissioned to design the church and he made use of both the frigidarium and tepidarium structures. He also planned the main cloister of the charter house. A small cloister next to the presbytery of the church was built, occupying part of the area. After 1575, starting under Pope Gregory XIII, several remaining halls of the baths were converted into grain and oil stores for the city of Rome.

After Rome became part of the Kingdom of Italy, its seat of government was moved to the city. In 1884, the Carthusians abandoned the charter house and the area around the baths was subject to substantial changes.  Roma Termini was built, the Ministry of the Economy moved to the area. A Grand Hotel and Palazzo Massimo were constructed. Gaetano Koch designed the palazzi fronting Piazza dell’Esedra (now Piazza della Repubblica), destroying part of the original exedra. Via Cernaia cut off the western gymnasium from the remains of the enclosure wall (the latter are now in Via Parigi). In 1889, the Italian government set up the Museo Nazionale Romano in the baths and in the charter house.


The enclosure of the bath complex took up 130,000 square metres or 32 acres of the district, about the same size as the Baths of Caracalla. The main entrance was to the northeast. To the southwest was a large exedra (now still visible as the outline of Piazza della Repubblica). The exedra was flanked by two large buildings, likely libraries. These in turn connected to circular halls: one of them is now the Church of San Bernardo, the other is visible at the start of Via del Viminale. The central block of the baths was 280 (910 feet) by 160 meters (520 feet) or 10.85 acres (compared to the 6 acres of the Baths of Caracalla).

The central block consisted of frigidarium, tepidarium and caldarium along a single axis, with other halls arranged symmetrically around them. Flanking the frigidarium were two open-air gymnasiums (remains of the western one are accessible at Via Cernaia). Two octagonal halls flanked the caldarium,

Much greater than the Baths of Diocletian 

Despite their similar size, the capacity of the Baths of Diocletian was said to be much greater than the Baths of Caracalla. This could be because the entrance and rooms were made larger than its predecessor in block size, which allowed more space and functionality.  According to Olympiodorus, the baths were able to hold up to 3,000 people at one time. However, this claim is disputed because Olympiodorus never described how he calculated this figure.

The frigidarium

The word frigidarium originates from the Latin word frigeo, which means “to be cold”. The prominence of the room and its conjoining rooms showed the increase in popularity cold baths had during the early 4th century compared to the hot baths. This also could have been a result of the depletion of the surrounding forests, resulting in a lack of fuel. The frigidarium, or Cella frigidaria consisted of a pool and a host of smaller baths connected to the main room. Water entering the room would come from a pipe or cistern and would exit through a drain within the pool. The water from the pool was thought to have been reused to flush latrines within the complex. The frigidarium was used mainly as a swimming pool or a cold-water bath, depending on the time. Normally, one would continue on to the frigidarium after using the hot-water baths or after exercising in the palaestra. Noting the massive size of the room, it was believed to have also been used as a social room. This idea is supported by the presence of statues and elaborate niches along the walls.[6] On each end of the frigidarium are large shallow pools that were made to be open-air bathing pools.

The caldarium

The word caldarium comes from the Latin word caleo, meaning “to be hot”. The purpose of the caldarium was that of the principal bath chamber within the baths. From its namesake, the room was used for a hot-water bath or for saunas or steam rooms. The room could have also been used for oiling before or after a bath, but, in most cases, this was moved to a separate room of the caldarium.

The caldarium, or cella caldaria, was rectangular in shape with many octagonal rooms found near it in the corner of the structure. The area seemed to be referencing the older Baths of Nero and Titus in its initial design. What set this caldarium apart was the sheer scale of the room compared to its predecessors. It continued a basilica-like theme from the frigidarium with a cross-vaulted middle bay and three projecting apses. These architectural techniques created the feeling of a more open space for the patron. Dressing rooms, also known as apodyteria, were located on either side of the caldarium. Along the sides of the caldarium were private rooms that are believed to have had multiple functions, including private baths, poetry readings, rhetoricians, etc. Other areas attached to the caldarium were a garden, lounging rooms, gymnasiums, and small halls and semicircular exedrae used as lecture and reading rooms.

Presence of libraries

Rectangular halls connected to the hemicycle have been suggested to be libraries because of their similar set-up to those in the Baths of Caracalla.  Historians, to support this theory, have demonstrated that these halls with their niches could properly house books from that day. References to the presence of libraries within the Baths of Diocletian both confirm and contradict themselves, such as the case of the author of the life of Probus. In it, he mentions that part of the Bibliotheca Ulpia, which are found in the Forum of Trajan, are being housed within the baths; a statement he later contradicts when later referencing the Bibliotheca Ulpia. However, with the presence of similar rooms that suggest that they were libraries found in the Baths of Caracalla and the Baths of Trajan, it is not a stretch to theorize that the baths of Diocletian contained a library.

Ancient Roman Bathing

The Romans emulated many of the Greeks’ bathing practices, and surpassed them in the size of their baths. As in Greece, the Roman bath became a focal center for social and recreational activity.

By constructing aqueducts, the Romans had enough water not only for domestic, agricultural, and industrial uses, but also for their leisurely pursuits. Aqueducts provided water that was later heated for use in the baths.

The vast amount of water needed for the larger baths was regulated by huge reservoirs in the baths complex. The reservoir of the Baths of Diocletian in Rome, for example, could hold 20,000 m³ of water.

Early baths were heated using braziers, but from the 1st century BCE more sophisticated heating systems were used such as under-floor (hypocaust) heating fueled by wood-burning furnaces (prafurniae). This was not a new idea as Greek baths also employed such a system but, as was typical of the Romans, they took an idea and improved upon it for maximum efficiency. The huge fires from the furnaces sent warm air under the raised floor (suspensurae) which stood on narrow pillars (pilae) of solid stone, hollow cylinders, or polygonal or circular bricks. The floors were paved over with 60 cm square tiles (bipedales) which were then covered in decorative mosaics.

Walls could also provide heating with the insertion of hollow rectangular tubes (tubuli) which carried the hot air provided by the furnaces. In addition, special bricks (tegulae mammatae) had bosses at the corners of one side which trapped hot air and increased insulation against heat loss. The use of glass for windows from the 1st century CE also permitted a better regulation of temperatures and allowed the sun to add its own heat to the room.

These Roman baths varied from simple to exceedingly elaborate structures, and they varied in size, arrangement, and decoration. In taking a Roman bath, the bather induced sweating by gradually exposing himself to increasing temperatures. To accommodate this ritual, all Roman bathhouses contained a series of rooms which got progressively hotter. Most contained an apodyterium—a room just inside the entrance where the bather stored his clothes. Next, the bather progressed into the frigidarium (cold room) with its tank of cold water, the tepidarium (warm room), and finally the caldarium (hot room). The caldarium, heated by a brazier underneath the hollow floor, contained cold-water basins which the bather could use for cooling. After taking this series of sweat and/or immersion baths, the bather returned to the cooler tepidarium for a massage with oils and final scraping with metal implements. Some baths also contained a laconium (a dry, resting room) where the bather completed the process by resting and sweating.

The layout of Roman baths contained other architectural features of note. Because wealthy Romans brought slaves to attend to their bathing needs, the bathhouse usually had three entrances: one for men, one for women, and one for slaves. The preference of symmetry in Roman architecture usually meant a symmetrical facade, even though the women’s area was usually smaller than the men’s because of fewer numbers of patrons. Usually solid walls or placement on opposite sides of the building separated the men’s and women’s sections. Roman bathhouses often contained a courtyard, or Palaestra, which was an open-air garden used for exercise.

Generally opening around lunchtime and open until dusk, baths were accessible to all, both rich and poor. In the reign of Diocletian, for example, the entrance fee was a mere two denarii – the smallest denomination of bronze coinage. Sometimes, on occasions such as public holidays, the baths were even free to enter.

Republican bathhouses often had separate bathing facilities for women and men, but by the 1st century AD mixed bathing was common and is a practice frequently referred to in Martial and Juvenal, as well as in Pliny and Quintilian.

Roman bathhouses offered amenities in addition to the bathing ritual. Ancillary spaces in the bathhouse proper housed food and perfume-selling booths, libraries, and reading rooms. Stages accommodated theatrical and musical performances. Adjacent stadia provided spaces for exercise and athletic competitions. Medical procedures may have occasionally occurred in the baths. Bathhouse visitors may have undergone some dentistry.

Inside the bathhouses proper, marble mosaics tiled the elegant floors. The stuccoed walls frequently sported frescoes of trees, birds, and other pastoral images. Sky-blue paint, gold stars, and celestial imagery adorned interior domes. Statuary and fountains decorated the interior and exterior.

Thus the Romans elevated bathing to a fine art, and their bathhouses physically reflected these advancements. The Roman bath, for instance, included a far more complex ritual than a simple immersion or sweating procedure. The various parts of the bathing ritual (undressing, bathing, sweating, receiving a massage and resting), required separate rooms which the Romans built to accommodate those functions. The segregation of the sexes and the additions of diversions not directly related to bathing also had a direct impact on the shape and form of bathhouses. The elaborate Roman bathing ritual and its resultant architecture served as precedents for later European and American bathing facilities. Formal garden spaces and opulent architectural arrangement equal to those of the Romans re-appeared in Europe by the end of the eighteenth century.

National Roman Museum – Baths of Diocletian

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.

Opening times:

Open every day from 9.00 to 19.30.Last admission at 18.30.Closed Mondays (except Easter Monday and during the “Culture Week”), 25 December, 1 January.


Single ticket valid for 3 days at 4 sites (Palazzo Massimo, Palazzo Altemps, Crypta Balbi, Baths of Diocletian)Full price: € 7.00Reduced price: € 3.50 for European Union citizens ages 18 to 25 and for European Union teachers with tenure.Free:  Visitors 17 and under.


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