The building, currently identified by many researchers as a Byzantine hospital, was built during the 6th century AD. There are two main arguments suggesting the function of this building. Firstly, it is confirmed by the written source that emperor Justinian initiated the construction of a hospital in Pamphylia, and a healer named Kosma was supposed to be working in this hospital. However, the exact location of this building has not been specified and thus it is plausible to assume that it was built in Side. The second argument comes from the projects of hospitals built in later times by the Seljuk architects. They were constructed on a very similar plan and thus one may argue that the hospital in Side was used as an example.
The hospital in Side is a two-storey building and it consists of five elongated rooms, each covered with a barrel vault. Every room is divided into three sections, separated by arches. The rooms are connected with each other with interior doors. The main entrance and the stairs leading onto the first floor were located on the west side of the building, which has not survived to our times.
On the floor of the second storey some mosaics were discovered, which may indicate the existence of the terrace. On the interior walls in several rooms the remains of frescoes can be seen.
The Byzantine hospital has dimensions of 27 to 16.5 meters. The outer walls were built using the rubble taken from earlier buildings from Roman times, and the internal walls - from uniform blocks of stone, carved specifically for this site.