Imperium Romani

What Was a Roman Bath (Thermae)?

Questions Answered · 5 min read

A look at the apodyterium, frigidarium, tepidarium, caldarium, and the hypocaust heating system, the social ritual of Roman bathing, and the great imperial thermae of Caracalla and Diocletian.

A Roman bath was a public building, often vast and lavishly decorated, where citizens could bathe, exercise, conduct business, and socialize for the price of a single small coin. The word thermae referred to the great imperial bathing complexes — heated by a sophisticated system called the hypocaust — that grew up from the first century BCE onward, while the older balneae were smaller private or neighborhood baths. Bathing was a daily ritual for most urban Romans: it began with exercise and progressed through a carefully ordered sequence of rooms, each at a different temperature, ending with a plunge into cold water and a session of massage and depilation. To understand the social world that revolved around them, see Roman society and daily life; to understand the engineering, see Roman aqueducts.

The Sequence of Rooms

The Romans bathed in a strict progression through a series of rooms, each tuned to a different temperature and humidity. After the gymnasium, a bather would enter:

  • The apodyterium — the changing room, with niches in the wall for clothing, a slave called a capsarius often guarding the door, and a wooden bench
  • The tepidarium — a warm, dry room heated from below, where the body prepared for the heat. Walls were often stuccoed and painted, and the room was used for hair plucking and anointing with olive oil
  • The caldarium — the hottest and most humid room, sometimes with a small heated pool (alveus) for soaking, and a deep bronze or marble basin (labrum) for rinsing
  • The sudatorium or laconicum — a dry, intensely hot sweating room, sometimes a hemispherical dome with a hanging bronze disk that was pulled up or down to regulate the heat, after the model of the Spartan laconicum
  • The frigidarium — the cool room, usually the architectural centerpiece of the bath, with a large unheated pool for a final plunge, open arcades, and skylights

The order of hot and cold was a matter of medical debate. The physician Galen recommended working up from cool to hot and then returning to cold, while the poet Seneca the Younger, who bathed daily, complained about the cheerful contrast of the slap of cold water onto a sweating man.

The Hypocaust: Heating the Building

The technological heart of the Roman bath was the hypocaust, a system of raised floors and hollow walls that channeled the hot gases of a wood-fired furnace. The praefurnium, a stoke-hole at one end of the building, fed a fire whose flame passed under a raised floor of stacked tiles (the suspensura) supported on short pillars of stacked bricks called pilae; the gases then rose through flues in the walls, exiting through chimneys in the roof. The result was a uniformly warm building with floor and wall temperatures that could be felt through sandals. The system was invented, according to the architect Vitruvius, in the late Republic and refined by the engineers of the early Empire; the pilae of the Baths of Caracalla in Rome are still standing.

The Great Imperial Thermae

The most spectacular baths were imperial projects, given to the Roman people by the emperor and his name. Agrippa built the first great thermae in Rome in 25 BCE, in the Campus Martius, fed by a branch of the Aqua Virgo. Nero built smaller baths in the Campus Martius, and Titus added the great Baths of Titus on the Oppian Hill, whose decorations inspired the wall paintings later found in the buried city of Pompeii.

The peak of the tradition was reached in the early third century. The Baths of Caracalla (Thermae Antoninianae), inaugurated in 216 CE, covered more than 11 hectares and could bathe perhaps 6,000 people at a time. They contained a frigidarium with four colossal granite columns, a great marble-lined caldarium, two libraries, exercise yards, and a stadium for athletic contests. The water came from the Aqua Marcia via a dedicated branch, the Arcus Neroniani, and the bath’s drainage system was so efficient that archaeologists have used its plan to understand the great basilicas. The Baths of Diocletian, completed in 306 CE under the emperor Diocletian (and the great military reformer behind the Tetrarchy), were even larger — 14 hectares — and the frigidarium of those baths is now the Basilica of Santa Maria degli Angeli e dei Martiri in Rome, redesigned by Michelangelo in the sixteenth century.

Mixed Hours, Women, and the Slaves

The question of whether Roman baths were mixed is more complicated than the modern imagination assumes. Mixed bathing was the exception and was often the subject of complaint: the statesman Pliny the Younger, in his letters, expressed surprise that his wife wished to bathe in a public bath at all, and several emperors — Hadrian, Marcus Aurelius, Alexander Severus — issued regulations separating the sexes or restricting mixed bathing to certain hours. In practice, the women-only sessions were typically scheduled in the morning, and mixed bathing took place in the afternoon at certain baths. Slaves — known as balneatores — were not, however, separated: the caparii and tractatores of the male bathing halls were frequently boys and youths in service to richer patrons, and the Roman satirists delighted in the situation, calling baths the “stews of the Empire”.

Admission, Cost, and the Social Ritual

A bath typically cost a single quadrans — about a sixth of the daily wage of an unskilled worker in the early empire — although the great imperial thermae were gratis, free to all, paid for out of the imperial treasury. Slaves and the very poor bathed free in the public facilities in the Subura and around the Forum; the truly destitute might bathe in the laconicum at the lupana in the Sentinum. Bathers brought their own strigil — a curved metal scraper for removing oil and dirt from the skin — and a small flask of olive oil. A deversor stood ready to hand them a fresh towel. After the bath, the bather might walk through the Porticus Vipsaniae to a popina for oysters, and the poet Martial would meet them in the Forum, complaining that no one in Rome had time for literature.