This little temple is on the intersection of the Decumanus and Via dei Molini, facing the Decumanus. The masonry indicates that it is from the republican period, perhaps from the years 80-50 BC. To the west are some walls that were built much later. The temple was excavated during the First World War.

The temple rested on a podium of tufa blocks and opus reticulatum, with a tufa cornice (total height 1.78). The pronaos or vestibule measures 6.35 x 4.20. No traces remain of the staircase(s) leading to the vestibule. The cella is square (6.35 x 6.30). What remains is of opus latericium, evidently belonging to a rebuilding during the Imperial period. In the cella are the remains of a mosaic floor. Some white tesserae belong to an older phase. A new mosaic floor of black and white rectangles was made at a somewhat higher level. Against the centre of the back wall is a masonry base, which must have supported a statue. In the cella a marble altar was found with an inscription that, unfortunately, was removed in antiquity.

Near the temple a dedication to Neptune and the Dioscures was found on a small marble altar:

It is a dedication by Lucius Catius Celer, Praefectus Urbi, that is, a very high official from Rome. From ancient literary sources we know that the people of Rome, together with the Praefectus Urbi or a consul, celebrated a festival in honour of the Dioscures on the Isola Sacra between Ostia and Portus, on January 27. The temple of the Dioscures was in the north-west part of Ostia. The little temple that we have described may therefore well have been dedicated to Neptune, a deity protecting shipping, like the Dioscures.