The Tetrapylon Street ran north-south from the Tetrapylon to the Theatre, and was the main public thoroughfare on the east side of the city centre. Part of the street immediately south of the Tetrapylon was excavated in the 1980s and showed that there was also a desirable residential area adjoining the area to the east of the street. In the street colonnades and associated with rich apartments above were found a series of some twenty late antique figured pilaster capitals with putti engaged in various rustic activities. The current project to excavate further south to the Propylon of the Sebasteion was begun in 2008. Its aim is eventually to open this part of the street for visitors and to investigate the detailed archaeo-history of the site in late antique, Byzantine, Seljuk, and Ottoman times.
The street paving and colonnade are late antique, of c. AD 400. The east colonnade was two-storeyed with new or re-used columns below between new brick and masonry piers. The upper storey was arcaded and some of its double half-columns and brick arches were found collapsed on or embedded in the street paving. The lower storey housed tiled retail spaces, while rich finds from the upper floors include further pilaster capitals, coloured wall mosaics, elaborate bronze door knobs, bronze vessels, intaglio gems, and abundant window glass.
A tall masonry structure stands on the western line of the street, and an inscribed statue base that belongs in its single central niche was found in front of it in 2013. The text honours one Myon Eusebes Philopatris, one of the builders of the Sebasteion, for his construction of ‘the first bathhouse for the Council of Elders’ (to balaneion to gerousion prōton). A high-quality himation statue of the same period (early-mid first century AD) was found nearby in 2011 and probably belongs on the base. The Gerousian Baths were probably located behind the niched structure and the wall to its south.
The street colonnade collapsed in a violent conflagration in the early seventh century (610-617), after which medieval life resumed on top of the partly-cleared collapse. Further to the south, between the niched building and the Sebasteion, a Byzantine glass factory was found with large quantities of late Roman cullet, and an Ottoman installation probably for cloth dyeing. Current work on the street continues to the south of the Sebasteion Propylon, towards the back of the Agora Gate where a surviving tunnel gives access to the South Agora.