The so-called Doric Building is an irregular, squarish structure situated immediately east of the South Propylon. Originally, it had four Doric columns between the side walls on its north-facing front, which was 8.21 meters wide. Its eastern sidewall was placed further east than today.

In Roman times this little building was annexed to the East Bath complex, a heating chamber (hypocaust) of which lies immediately to the east. On that occasion, the walls of the building were moved and rebuilt, and the front was shortened from four to three columns. The original Doric entablature was still in use with its architrave, triglyph frieze and geison, of which some blocks are lying at the building. The remains inside the building indicated that a water basin occupied the inner half of the building in Roman times. In Byzantine times, the Doric Building may have served as a source of water for different purposes, such as washing before attending the Mass in the church.

Doric building from north.

This building was probably erected by Idrieus, which is indicated by an inscribed architrave block preserving the letters -OMNΩMY-, which is believed to be part of [IΔPIEYΣ EKAT]OMNΩ MY[ΛAΣEYΣ ANEΘHKE etc. (Idrieus son of Hekatomnos, from Mylasa dedicated etc.). This block is placed inside the building, but the inscription is only visible in favourable light. The building was, however, not completed; the columns never received their flutes (the vertical channelling). It seems to have had an open front without any cross-wall behind the colonnade, but the present side- and back-walls are not the original ones; the original function of this building may have been as a fountain-house.