The Early Byzantine baths were built in the 6th century during the reign of the Byzantine Emperor Justinian the Great (527–565).
During archaeological excavations, two-thirds of the baths' area has been discovered and explored – five warm rooms, two of which had semicircular bathing pools, a central hall, and a corridor. The remaining part now lies beneath the neighboring streets and houses.
The walls of the baths are constructed in "opus mixtum" (i.e., in layers of stone and brick) and covered with marble tiles. In some places, they have been preserved up to 3 meters high. The warm rooms had a suspended floor and a hipocaust. The most impressive feature is the central hall, where four massive marble columns supported a cross vault or dome. The floor was covered with marble.
The baths were supplied with water through a water pipe system that ran from the west side of the building.
In the 5th-6th centuries, a complex underground water supply network was built, spanning the entire city.
The baths functioned until the end of the 8th century. At that time, a brick wall was also built in the corridor (hall), narrowing it.
At the beginning of the 9th century, the baths were restructured. Many of the entrances between the rooms were further partitioned off and used for residential and household purposes. Kilns for lime production were built in the central hall. The marble tiles from the bath flooring and the marble paneling from the walls were used as raw materials.
The Byzantine chroniclers Theophanos (also known as the Confessor) and Patriarch Nikiforus report that the Byzantine Emperor Constantine V Pogonat received bathing treatment here in 680.
The thermal baths were discovered during archaeological excavations in 1973-1975 and 1998-2001. They have been restored and conserved.