Byzantine cities had public baths open to all citizens, regardless of social class, profession or gender. Apart from their central function as places for keeping clean, baths also served as meeting points and entertainment venues, where the inhabitants spend a great part of their day talking with their friends and family, eating together and having fun with music and dance. For women, who had few opportunities to appear in public, the baths were especially important. The emperors saw to the building of large baths (Thermae ), which mainly relied on state support for their running costs; residents also paid a small contribution in the form of a low admission fee (the Valaniko). On special occasions entry was free for all, as was the case at the Baths of Zeuxippos every May 11th, when the founding of Constantinople was celebrated.

In the Roman Empire, just as in ancient Greece, bath houses called for special architecture and systems to transport and heat water. They usually had vaulted roofs, so as to provide insulation and maintain the temperature of the hot air in the sauna rooms and the water flowing from taps in marble pools or bathtubs, basins and footbaths. Due to the fact that they were visited by many people, public baths were built in central locations. There were, however, private baths in the mansions of the wealthy, as well as others built within monastery enclosures. The small bath houses intended for hot baths were mainly private, known by the Ancient Greek name valaneia.  Large bath complexes were generally public buildings known as thermae, built with money from the emperor. They were monumental structures consisting of several different areas (central halls and rooms), lavishly decorated with marble walls and floors, mosaics , statues, paintings and images from nature or portraits of the emperors and their families. 

Byzantine baths maintained the organization of their Roman predecessors, containing three main areas: (a) the cold bath (psychrolousion or frigidarium), (b) the warm bath (chliaropsychrion or tepidarium), and (c) the area for the hot baths (zeston or caldarium). Cleaning took place in the hot bath, were the body perspired and was cleansed. The warm bath area served as an intermediate step between the hot and cold bath, allowing bathers to adjust to the temperature change. The frigidarium contained one or more pools of cold water for use after the hot baths.  This was the most suitable area for social events and gatherings, which is why it was usually larger than the other two. Depending on the size of the baths, there were smaller ancillary rooms leading off the main areas, for changing, body care (massage, waxing, etc.), depositories, stores, toilets, etc.

The hot baths (caldarium) were heated by an under floor heating system known as a hypocaust [= underground burning]. This system was constructed as follows: the floor of the hot bath area was elevated and supported on a dense grid of what were usually squat clay blocks (square balusters, approximately 20x20 cm); hot air from an external furnace that burned wood, charcoal or even petroleum (= Median fire, from the Medes, as the Byzantines named the Persians) was channelled into the underground area between the balusters. Clay pipes also channelled hot air from the floor into the walls for more even heat distribution in the room, so that the people coming in would sweat. Afterwards they would wash successively in hot and cold water. The water was carried through a dense network of pipelines from the pool or aqueducts to the baths for bathing and swimming, while other pipes drained off dirty water and detritus. In the cold and warm bath halls there was a constant supply of cold and warm water for bathing or washing. In contrast, the temperature increase caused by warm air circulating under the floor and inside the walls in the caldarium was desired in order to promote perspiration, like a modern dry sauna, while the running hot water gave off steam for inhalations, peeling and skin cleansing.

The baths were open every day of the week, including Sundays, except in cases of drought, earthquake or war. They remained open until late in the evening, and at quieter times (noon or late evening) were visited by people suffering from illness. In most baths there were separate areas and entrances for men and women, or different opening hours and days. It does however seem that mixed baths did exist, despite protests from the Church Fathers . These baths appear to have been abolished after the 7^th century.

Medical books of the time specified the frequency of bathing. For example, baths were recommended no more than four times in January, six times in March and eight times in April. The number of baths per year allowed for a monk was prescribed by the typicon or rule of the monastery he belonged to, and varied from one monastery to the other. However, monks often went unwashed as a sign they had renounced the pleasures of life. Despite the severity of Church restrictions on the use of baths, some clergymen did visit them.

From the 7th century onwards large bath houses fell into disuse, and were eventually abandoned due to population shrinkage, high maintenance costs and lack of resources to ensure water supply. This resulted in a significant reduction in their number and size in all cities including the capital. Very few Byzantine bath houses from this time have survived to the present day: one Palaeologan era paired secular bath is preserved in Ano Poli (the Upper City) in Thessaloniki, but the majority of baths that can be dated to Middle and Late Byzantine times belong to monasteries. The general trend was bucked by baths in the palaces of Constantinople and in aristocratic circles, as evidenced by the founding of baths by Leo VI . Unlike the Byzantines, among whom frequent bathing was taken for granted, in the West it was seen as a sign of illness. Sent to marry King Otto II of Germany, the Byzantine princess Theophano was accused by her contemporaries of frailty on account of the frequent baths she took!