Engineering Rome

The Baths of Caracalla – A Case Study on Water Management


Baths were a huge part of ancient Roman culture. Not only were they one of the hallmarks of Roman engineering, but they were how citizens of any status would meet, socialize and get clean. It was also a huge flex of Roman culture and power since they were using millions of liters of water for purely luxurious reasons. Plenty of bathhouses have survived the years, leaving behind magnificent ruins that still stand today. These bathhouses included “a wide diversity of rooms with different temperatures, as well as swimming pools and places to read, relax and socialize” (Cartwright). They were also “important drivers in architectural innovation, notably in the use of domes” (Cartwright).

With its magnificent arches, warm brown color against a bright blue Italian sky, and a powerful aurora of having lived through thousands of years, the Baths of Caracalla left an impression on me. While it would have been impressive to see what the place looked like when it was lavishly covered in marble and mosaics, it is equally as stunning stripped of its decorations. Its sturdy skeleton has withstood the test of time, but what really struck me was not its present state, but its past one, when gallons upon gallons were flowing through the place.

The building was already an engineering feat, but to have an aqueduct bring water to it, have a cistern store it for continuous use, have the multiple massive pools be constantly full, and then have water flow from there to running toilets to then be flushed away back to the Tiber river… now that’s an impressive system, and it was a little under two thousand years ago.

Figure 1. A striking photo of the Baths at golden hour. If the ruins are this beautiful, I can’t imagine what it looked like in its prime!

History of the Baths of Caracalla

The Baths of Caracalla were built for mostly political reasons. They were made between 212 A.D. and 217 A.D. by Emperor Caracalla on the Aventine, with the external enclosure’s work being done by Elagabalus and Severus Alexander (ArcheoMe, 2020). “They were considered an architectural and engineering marvel, especially when you consider their date of construction, water supply, and heating and drainage systems”(ArcheoMe, 2020). They were covered in marble, tiles and mosaics. Here is a cool, quick video tour of how they most likely looked back in the day.

Emperor Caracalla most likely built the place to please his people, and to make them like him (this was a big motivator for emperors to build things in ancient Rome). The Baths could hold “as many as 10,000 people daily” (Deming). At the time, it was Rome’s biggest bathing complex, standing at 40 meters tall, with an area of 100,000 meters squared (Baths of Caracalla). They were beat out almost a hundred years later by the Baths of Diocletian in 306 A.D.

The Baths were in operation for over 300 years, with that finally ending in the 530’s when Barbarian attacks on Rome destroyed Aqua Marcia (The Romans Baths), the aqueduct which fed the Baths of Caracalla.

Figure 2. A model of the Baths
Figure 3. Entrance to Baths of Caracalla
Figure 4. Inside the Baths of Caracalla, present day

From the Upper Anio Springs to the Cisterns of the Baths of Caracalla

Thousands of gallons were needed to supply the Baths. All of the water in Rome came from the source (such as a spring or lake) to the destination via an aqueduct, which was like a giant track for the water to travel on. There were no pumps to move the water, so the aqueduct had to be sloped downwards the whole way so the water could constantly be moving. (See this video for more information on how aqueducts were made, as well as their distribution networks and maintenance.) Aqueducts were very important because if they were damaged by anything or destroyed by invaders, it would stop the flow of water, therefore hurting the city and its people.

The aqueduct that fed the Baths was from a branch of Aqua Marcia called Aqua Antoniniana. This branch was built in 212 A.D. and enhanced with a new spring (ArcheoMe, 2020). Aqua Marcia was built between 144-140 B.C., and its water source was primarily from springs, therefore letting it provide very high-quality water. The water was from “the slopes of the Simbruini ridge west of the valley” (Aqua Marcia,). It also had a “water capacity that was equivalent to 1/24ths of the total water supply of Rome” (Logistics). It was 57 miles long and its volumetric flow rate was 78 cubic feet per second, or 2208.71 liters per second (Steve Muench, 2022). Olympic-sized swimming pools can hold 2.5 million liters of water, so this flow rate could fill the swimming pool in just under 20 minutes!

Figure 5. A map of Aqua Marcia

There aqueducts were most commonly supplied by groundwater instead of surface water (Deming, 2020). When the Romans “tapped a spring for an aqueduct, they typically augmented the flow and supply by driving tunnels (also called adits) into the surrounding terrain” (Deming, 2020).

The water would arrive “at an enormous cistern divided into eighteen compartments and a capacity of 80,000 cubic meters [80,000,000 liters]” (Baths of Caracalla – Data, Photos & Plans, 2020). It was then lowered “via gravity to tubes and crossed the gardens on its course to the building” (Baths of Caracalla – Data, Photos & Plans, 2020).

The water was always flowing into the Baths and was even stored at night. “Large bath complexes could also be complemented by a reservoir cistern that was filled overnight so as to provide additional flow during daily operational hours” ( Deming, 2020).

Figure 6. The walls of one of the underground aqueducts

The Aqua Marcia was 0.9 meters wide and 2.4 meters tall. These dimensions were determined not for the flow of water but for the need for maintenance (Deming, 2020). The water almost always contained significant quantities of dissolved minerals, making it hard. (Deming, 2020). This caused deposits of sinter over time that needed to be removed. If not, it would choke off the flow (Deming, 2020).

Figure 7. A sketch of the overall flow of water into and out of the Baths. The double line between the aqueducts represents the branching off from Aqua Marcia to Aqua Antoniniana.

Water within the Baths

There were four main bath areas, in which the temperature of the water goes from hot to cold. First, there was the caldarium, which was a hot sauna. Second, the tepidarium, which was a warm pool. Third, a frigidarium, which was a much colder pool, and lastly, a swimming pool, called a natatio (Livingston, 2022).

Figure 8. A diagram of the thermal path in the Baths of Caracalla

 The hot sauna/hot bath area was a giant circular room, with several columns supporting its dome roof. The room received plenty of sunlight through its large windows (Baths of Caracalla – Data, Photos & Plans, 2020). The tepidarium was next, and this is where the caldarium bathers would go for a warm bath. The frigidarium was an indoor swimming pool used for cold baths. It was as large as today’s Olympic swimming pools (Baths of Caracalla – Data, Photos & Plans, 2020).

The frigidarium also had multiple “fountains and pools, two of which are now located in Palazzo Farnese” (Mingoia, 2022 ). They were moved in 1621 to their current spot (Fontana Di Piazza Farnese (Rome)).

The water was heated by fireplaces on the lower floors, where the hypocaustics spread hot air in cavities under the floor, supported by short brick pillars (ArcheoMe, 2020). This method was also seen in Ostia Antica. (See here for a short video on how hypocaustics work.) The water was “heated in massive copper tanks and fed through the baths in a network of lead pipes before draining away” (The Subterranean Galleries of the Baths of Caracalla). “Approximately 9,000 men were needed to operate the baths on a daily basis” (Livingston, 2022). The water in the baths were heated by slaves. In order to keep the water in the caldarium hot, the slaves “tended to 50 underground ovens 24 hours a day” (The Subterranean Galleries of the Baths of Caracalla). The ovens also required “approximately 10 tons of wood to be carted into the city each day just to heat the water” (The Subterranean Galleries of the Baths of Caracalla).

Figure 9. A pool in Caracalla
Figure 10. A Bath from Caracalla in Piazza Farnese

Water Exiting the Baths

After the water was used in the Baths, it was used to flush the toilets. “Waste water from a bath or overflow from a fountain would have been ideal for flushing a public toilet” (Deming, 2022). The water would have gone in one direction across all of them, taking all the waste with it. It would have eventually gone from the main sewage system, through the Cloaca Maxima (an even bigger sewage system!) and then the Tiber River (Sanitation in Ancient Rome, 2022).

Figure 11. Toilets in Ostia Antica, similar to the ones that would have been in the Baths of Caracalla. Water would run perpendicular to the seats, flushing away waste.


The Romans were masters of structures, but it is seldom remembered how well they managed other things, including water systems. The Baths had a water system ahead of its time. Thousands of gallons coming in and out of an enormous facility, and even though the water was not used for survival, every drop had a destination. Either it went to a pool, a fountain, for steam or eventually to flush the waste. If only I could have seen the place with the water flowing!

Works Cited

“Aqua Marcia.” Roman Aqueducts: Rome Aqua Marcia (Italy),

ArcheoMe, Redazione. “Archaeology: The Baths of Caracalla, Wellness Center of Antiquity.” ArcheoMe, 26 Nov. 2020,

“Baths of Caracalla.” Wikipedia, Wikimedia Foundation, 23 Oct. 2022,

Cartwright, Mark. “Roman Baths.” World History Encyclopedia,

Deming, David. “The Aqueducts and Water Supply of Ancient Rome.” Ground Water, Blackwell Publishing Ltd, Jan. 2020,

“Fontana Di Piazza Farnese (Rome) – All You Need to Know before You Go.” Tripadvisor,

Livingston, Leslie. “Guide to the Baths of Caracalla in Rome.” The Geographical Cure, 5 July 2022,

“Logistics.” Omeka RSS,

Mingoia, Jessica. “Baths of Caracalla.” Smarthistory, 10 June 2022,

“The Roman Baths of Caracalla.” The Roman,

“Sanitation in Ancient Rome.” Wikipedia, Wikimedia Foundation, 25 Oct. 2022,

“The Subterranean Galleries of the Baths of Caracalla.” Time Travel Rome, 20 June 2019,

“✅ Baths of Caracalla – Data, Photos & Plans.” WikiArquitectura, 23 Sept. 2020,

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