On the entablature surmounting the Ionic columns are panels containing medallions of Scots sovereigns from James I.
The central area, where is the basin of the font, is an octagon around which stand eight porphyry columns, with marble capitals and entablature of classical form; outside these are an ambulatory and outer walls forming a larger octagon.
While it was probably badly wrecked by the Romans at the sack of the city, its massive columns with the entablature survived.
Their bases and shafts are not finished, though the capitals and rich entablature seem completely worked.
In height and of the Corinthian order, and supported an entablature 7 ft.
On the entablature is inscribed the words Aux Grandes Hommes La Patrie Reconnaissante.
The frieze of the entablature contains sculptures only in the metopes of the east front and in those of the sides immediately adjoining it; the frontal metopes represent the labours of Heracles, the lateral the exploits of Theseus.
Only the lower part of the cella wall was of stone, the rest being of unbaked brick; the entablature above the columns was of wood covered with terracotta.