During the relatively peaceful second century Odessos grew into a major economical and cultural centre of the Black Sea coast and the Roman province Moesia Inferior. Close to the end of the century the blossoming city could afford the enormous construction and maintenance operations. The daily life of the Roman citizens included visits to the baths called thermae. They were also equipped with gymnastics and sport halls, called palaestras, meeting and discussing halls, relaxation room, etc. In addition to the indoor hall, the thermae had a featured real palaestra - a big yard, surrounded with columns and shops. The palaestra is in the north part of the baths and stair lead from it to the main hall.

The building of the Roman thermae was designed symmetrically, and the arrangement of the rooms follows the recommendation of the Roman architect Vitrivius. Thus, the warm rooms face south, and in the middle of the southern facade is the caldarium - the hot water bath. The two entrances can be found on the northern side of the thermae. Wide stairs lead to the lobbies - with the purpose of preventing the cold air from the dressing rooms. The dressing rooms (apoditeria) on the other hand were large enough to fit all visitors and provide comfort. This is where the slaves would stay and keep the clothes and jewels while the citizens of Odessos enjoy the baths.

The highest preserved part of the thermae - the Roman tower was one of the walls of the western apoditeria. The first phase of the bath procedure was the so called "short bath" - the visitors went through the frigidarium (hall with cold baths), tepidarium (warm bath) and eventually got ready for the main hot bath in the caldarium. It includes one spacious pool and two smaller along the walls - all three of them receiving water from the boiler halls. Those citizens, who were willing to enjoy "the full program", continued to the actual tepidarium, and eventually in the actual frigidarium. In this way the body was refreshed and prepared to go back to the cold baths' halls. All halls were located so that the simultaneous enjoying of the baths by men and women would be prevented.

In order to perform their functions, the baths are equipped with the necessary devices and rooms. In the southern part was located the prefurnium - that is where the water and air for the baths were heated up. The warm rooms are featured for their double floor. The upper surface is constructed upon vertical columns. The hot air circulates between them and warms up the floor. The rooms are heated in the same way from the air, transmitted between the walls and the marble surface.

Along the east and west walls we can find the passages, used as wood stock rooms, and in the southern end was the bathroom. A few shops for the visitors were located on the level above the passages. In the northern end, a huge water container was utilized, from which the water would flow towards the boiler room. Afterwards, ceramic pipes take the water to the sinks and the pools. The outgoing foul water canals were built in under the floors. Their disposition brings the foul water into the sea.

The building itself was about 20 meters high (the preserved part of it nowadays - the Roman tower is 18 m high), constructed from both stones and bricks. The outer walls and the halls were decorated with marble columns, ornaments and other architectural elements. Another feature is the number of statues of distinguished citizens and Roman gods, built up together with the needed fountains. The social and political crisis from 3rd century caused damages in the Roman Empire and Odessos, as a part of it. The maintenance of the baths became very expensive and they gradually left without good care. The stone material and decorative elements were taken and used for the construction of other buildings, including the small baths of Odessos from 6th century.