Baths Fit For An Emperor

By Ines Arletti, July 4, 2010

The Baths of Diocletian in Rome

The Baths of Diocletian in Rome

The Roman Baths of Diocletian are said to have been among the most majestic and perfect in all the ancient world. Conservator Ines Arletti offers an insider's view.

“Take time out to regenerate mind and body in the luxurious surroundings of the Diocletion Spa baths. A wide range of activities and services are available – including hydrotherapy, beauty treatments, stress management, sport, diet and fitness as well as music and poetry recitals and access to our library of rare books. Come in and treat yourself in our exclusive spa baths – decorated by top level designers and craftsmen and heated using the latest in alternative technology….”

Such may have been the wording of a hypothetical brochure advertising the delights available at the vast monumental thermal complex in the heart of Rome. Located in one of the city’s most significant archaeological zones, the Baths of Diocletian cover an area of 130,000 square metres and it is said that their capacious halls could accommodate around 3,000 clients at any one time.

Completed in an extraordinarily short time (298-306 AD), the Baths were built by Maximinianus and named after his co-emperor Diocletian. The organization of such a massive project would certainly have been a formidable and expensive undertaking, even though labour costs at the time were extremely low. Some sources refer to a veritable army of workmen numbering some 40,000 souls and to this number must be added all those involved in the various phases of planning and preparation: millions of bricks had to be made, and tonnes of sand, pozzolana and lime had to be sourced and delivered. Workmen in the marble pits of Egypt and Greece quarried and pre-worked the marble slabs which were then sent by sea to Rome, where expert craftsmen carved and sculpted fine columns, ornate capitals and decorative wall mounts. Talented artists and artisans decorated the floors, the walls and the vaulted ceilings with brightly coloured mosaics, wall paintings and ornamental stucco. Who knows how many trees were felled to provide timber for the scaffolding used in building the arches and vaulted ceilings? Then there were the many people who laboured to provide food for the workmen; to produce tools for the construction and to ensure the smooth functioning of such a vast building site. The orchestration of the whole project must have been impeccable for them to complete such a massive and complex structure in just eight years.

Edmond Paulin's fantastical recreation of the Frigidarium in the Baths of Diocletian (detail)

Edmond Paulin’s fantastical recreation of the Frigidarium in the Baths of Diocletian (detail)


The “Acqua Iovia”, a branch of Rome’s grand “Acqua Marcia” aqueduct, was built specially to supply water to the baths, which also boasted a external water cistern known as the “Botte di Termini” (with a capacity of 7,000 cubic metres) as well as several water tanks within the complex. A complicated heating system operated both under the floors and in the walls: hot air from the ovens was directed through the hollow spaces between the suspensurae (small pillars supporting the floors) and drawn through terracotta pipes in the intramural cavity.

The thermal bath was an articulated construction of antique origins – in fact evidence of the building of thermal baths – initially intended as a place for public ablution and physical well-being – dates back to the archaic period in Ancient Greece, where areas for gymnastic activities were provided with pools, to be used for washing after the physical exertion was over. Separate areas designated for ablution and relaxation were already a feature of bath houses in Classical antiquity. In the Roman world, in the Forum Baths in Pompei (end of 1st century BC), there is evidence of a section reserved only for women – obviously the smallest and least attractive! Over time, the areas dedicated to physical well-being became larger and ever more sumptuous, and were decorated with spectacular works of art – such as the heroically-scaled Farnese Hercules made for the Baths of Caracalla and currently displayed in the National Archaeological Museum in Naples; or the Laocoön Group sculpture from the Baths of Trajan; or the large bronze statues of the Resting Pugilist (Il Pugilatore) and the Hellenistic Prince from the Baths of Constantine now on show at the Rome National Museum in Palazzo Massimo. The splendour of every new thermal spa bath reflected the munificence of each successive emperor, as well as their populist policies, opening up these centres of repose and culture to the common people.

After those of Trajan and Caracalla, the Baths of Diocletian are said to be the most majestic and perfect in all the ancient world. A large square enclosure (380m by 365m) was surrounded by circular halls (probably libraries containing Greek and Latin texts), apsidal and rectangular rooms, areas for leisure and cultural activities and a large exedra at the centre of the south-western side. (The exedra which today can be found in Piazza della Repubblica – constructed by Koch in the mid-19th Century – traces the walls of the original bath complex using their foundations). Extensive, well-cared for gardens filled the space between the outer perimeter and the thermal baths proper. The heart of the complex consisted of a central axis along which lay the Calidarium, the Tepidarium, the grand Frigidarium, and finally the Natatio or swimming pool. Vestibules, gymnasiums and service areas were located laterally along the axis.

This floor-plan of the Baths created 1893-1901 by Rudolfo Lanciani shows the Calidarium(1), Tepidarium(2), Frigidarium(3), Natatio(4), Palaestrae (Gymnasiums)(5), Entrance(6) and Exedra(7)

This floor-plan of the Baths created 1893-1901 by Rudolfo Lanciani shows the Calidarium(1), Tepidarium(2), Frigidarium(3), Natatio(4), Palaestrae (Gymnasiums)(5), Entrance(6) and Exedra(7)


The Calidarium was a rectangular space (21m x 47m) with apses at the centre of each side. Oriented to the south-west in order to take advantage of the highest concentration of the sun’s rays, it was the warmest room in the complex – so much so that footwear had to be worn in order to avoid unpleasant burns to the feet. There were seven hot water pools within the Calidarium, while a large basin filled with cold water at the centre of the room was used for cooling down between immersions. Alongside the Calidarium were two saunas, one a steam bath (sudatorium) and the other a dry sauna (laconicum). The bathing pools and the walls were lined with valuable marbles and the ceilings would have been richly decorated with painting and stucco. All that remains today of this section of the baths is the northern apse, which now forms the entrance to the Basilica of Santa Maria degli Angeli.

The Tepidarium was a smaller, semicircular room 22m in diameter, which was designed to gradually modulate body temperature while passing from the Calidarium to the Frigidarium. Lit by natural light from eight 12-metre-high windows, the majestic Frigidarium (61m x 42m) had cold water pools set around its perimeter. This space too was lavishly decorated, with grand pink marble columns topped by elaborately carved capitals supporting the magnificent cross vaulted ceiling. Today it is the Basilica of Santa Maria degli Angeli, together with the Tepidarium which forms the vestibule.

However the major attraction was undoubtedly the Natatio, a huge rectangular open-air swimming pool (measuring around 4,000 square metres), lined with precious marbles. Monumental facades bordered its length, while porticoes enclosed each end of the pool. Of particular note is the south-facing facade made up of five enormous niches separated by alternating curved and rectilinear walls, which were completely covered with marble slabs, multicoloured mosaics and decorated with statues.

Conservators and researchers are still uncertain about how some areas of the Baths were used, even though new clues are continually being brought to light via restoration works that have been going on for years. However what is certain is that the vast thermal complex would have been an astounding sight. French architect Edmond Paulin, who worked on a project to restore the Baths in the late 19th century, drew up a detailed visual reconstruction of the interior decorations. The elaborate and multicoloured mosaics and paintings he portrays may seem kitsch and over-the-top to modern eyes, but the fragments remaining of the interior wall cladding would seem to lend weight to the plausibility of Paulin’s dazzling recreation.

Ines Arletti works as a conservator for the Soprintendenza Speciale per i Beni Archeologici di Roma. She is currently part of a group working on conservation in the Museum of the Baths of Diocletian

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