At the south end of the Forum are the confusing remains of a temple, the counterpart of the Capitolium. All that remains is the substructure, consisting of corridors and little rooms (opus reticulatum). The temple was dedicated to the goddess Roma and to the deified Emperor Augustus. It was erected during the first part of the reign of Augustus' successor, Tiberius (14-37 AD).
A priest nominated for life, the flamen Romae et Augusti, was in charge of the cult. It was a function reserved for the elite. He was supported by a temple-keeper (aedituus). From an inscription we know the name of one of these: Q. Ostiensis Felix, a freed slave of the town.
The height of the building must have been some 16 m. It was lavishly decorated with marble (cornice, frieze, architraves, pediment, ten columns). The building provides the first example in Ostia of the extensive use of this material, and thus shows the influence of Augustan Rome. Fragments have now been attached to a modern wall to the east of the temple. In front of the same wall is a statue of Victoria, possibly flying, that may have been on the ridge of the roof of the temple. On top of the substructure is a cult statue of Roma Victrix, dressed as amazon. Her left foot is resting on the globe. The statue was found in the building and is one the reasons for the identification of the temple, that is now generally accepted. It was still being discussed in the early 20th century, when the building was known as Temple of Ceres.
The cella was approached via staircases on the sides, perhaps because the front part of the temple was used as a speaking platform by orators or judges. From an inscription we know that occasionally the city council met in the temple (CIL XIV, 353: In aede Romae et Augusti placu[it] ordini decurionum ...).
During the reign of Hadrian two brick arches were built on either side of the south end of the temple. These allowed the passage of pedestrians only.
Plan of the temple. After SO I.