Cleanliness is one of the achievements of urban culture, for the forced cohabitation of many people in confined spaces calls for hygiene and decency. Baths thus became a distinctive feature of urban life in Greek and Roman Antiquity from early on, as few houses had their own water supply. Yet bath houses offered much more than just cleaning the body: they were hubs of social life, meeting points and entertainment venues. City dwellers spent much of their day there, since apart from washing they could enjoy the relaxing properties of water, meet up with friends and acquaintances, talk about business, catch up on news and exchange ideas. For women, who had few opportunities to appear in public, going to the baths was a chance to display their finery and bathing utensils, as well as to engage in conversation, dance and sing songs.

Bath houses, also known as valaneia, were buildings of unique architecture that made use of special technology to transport, use and heat water. The thermae or bath houses in imperial cities were public buildings often of monumental character. They were entire complexes of large halls and small rooms, lavishly decorated with marble walls and floors, mosaics and statues, paintings and images from nature and imperial iconography. Private baths also existed, but they were smaller and only offered the basic facilities found in the large thermae. The toilets and changing rooms were in the antechamber, where people changed their clothes, leaving them in the custody of attendants known as kapsarioi. There followed a series of rooms, either in a row or at right angles to each other – areas for the cold bath (psychrolousion or frigidarium), the warm bath (chliaropsychrion or tepidarium), and finally the area for the hot bath (zeston or caldarium). In the changing rooms there were clothes racks and changing benches; the cold rooms had small pools for preliminary cleaning and taps for footbaths and body washing, while in the hot baths the body perspired and was cleaned for the last time. If they wished, bathers could then have a cold bath before drying off, being anointed with unction and getting dressed.

The hot baths were heated by the hypocaust, a system that used a very low basement below a raised floor resting on dense rows of small piers or poles. Air heated in an adjoining charcoal furnace (prefurnium) circulated in the area under the floor, as well as in the walls and vaulted roof: clay pipes (tubuli) embedded in the walls allowed hot air to rise, cool and descend to the floor again. Air circulation and a continuous supply of fuel helped maintain the high temperature in the hot bath.

The baths were open all days of the week including Sundays, except in the case of drought, earthquake or war. They were visited by men and women of all ages and social class, usually in the mornings or evenings, though also on occasion at night, when they were illuminated by oil lamps. Most bath houses were in pairs, with two separate entrances and wings, one for each sex, but used a common hypocaust for fuel economy. If the bath was not paired then men and women used it at different times and days. There is, however, evidence for the existence of mixed baths, despite protests from the Church Fathers . Even since Roman times the use of mixed baths had been seen as a sign of moral laxity, and emperors such as Hadrian, Marcus Aurelius and Alexander Severus forbade members of the opposite sex from bathing at the same time. Visitors paid an admission fee, the valaniko, the value of which varied down the centuries. Admission was free on special occasions: the baths of Zeuxippus in Constantinople opened for free on 11^th May every year to celebrate the city’s inauguration.

Doctors and medical books of the time recommended frequent bathing. According to them, this was advocated no more than four times in January, six times in March and eight times in April. Similarly, the number of baths allowed for a monk per year was prescribed by the typikon or rule of the monastery he belonged to, and varied from one monastery to the other. Despite the Church’s strict stance on limiting bath house use so as to avoid excess, and the stress placed on going unwashed as an ascetic virtue, even clerics would visit the public baths, and several Church Fathers spoke favourably of them.

From the 7th century onwards the large thermae fell into disuse, and were eventually abandoned due to population shrinkage, lack of resources to ensure water supply and high maintenance costs.  This resulted in a significant reduction in their number and size, not only in the capital but also in provincial cities. Very few Byzantine bath houses from this time have survived to the present day: one paired secular bath from the Palaeologan era is preserved in Ano Poli (the Upper City) in Thessalonica, but most of the remaining ones belong to monasteries. Nevertheless, whether luxurious or not, the bath house tradition was maintained in the palaces of Constantinople and in aristocratic circles in general, as evidenced by the foundation of baths by Leo VI . Unlike the Byzantines, among whom frequent bathing was taken for granted, in the West it was a sign of illness. Sent to marry King Otto II of Germany, the Byzantine princess Theophano was accused by her contemporaries of being frail on account of the frequent baths she took.