On the southern, vertical side of the rock of the Acropolis, above the Theatre of Dionysus, stands the choragic monument of Thrasyllus. According to the inscription on the architrave, the monument was erected by the choregos Thrasyllus in 320/19 BCE, after a victory in the dithyrambic competition for men. From a later choragic inscription we are informed that the structure’s upper part was remodelled in 271/70 BCE by the agonothetes (the responsible for the athletic or artistic competitions in religious festivals) of the Great Dionysia, Thrasycles, son of Thrasyllus, who founded two more pedestals on the monument’s entablature for the dedication of tripods.

The monument of Thrasyllus, or Thrasylleion, essentially consisted of a facade adapted to the opening of a cave-like recess. This marble-built facade, resembling a temple facade, consisted of a pillar between two antae, which created two large openings/doorways. Its superstructure consisted of the architrave with the inscribed dedicatory inscription, the frieze decorated with olive and ivy wreaths, and the cornice on which the bases for the tripods were placed. A variety of materials was used for its construction, including stone from the coast of Piraeus, limestone, marble of island origin, Pentelic marble, and Hymettian marble.

The choragic monuments of the dithyramb contests were initially simple in form and consisted of the pedestal, the base and the tripod given as a prize. However, after the mid-4th century BCE and in the context of the aesthetic values of the time, they began to acquire more monumental dimensions and take the form of naiskos-shaped buildings, such as that of Thrasyllus.

The monument of Thrasyllus was transformed into a Christian church, possibly in the 11th century. Scholars believe that the establishment of the sanctuary was due to the sheltering capacity of the cave and not to an attempt to purify the pagan past. The church was called Panagia Spiliotissa/ Chrysospiliotissa and some of its remains are preserved inside the cave today.