The masonry of this Guild Temple (opus latericium) has been dated to the reign of Commodus. It was accessible from the Decumanus along a staircase running parallel to the facade, leading to a door 3.50 wide, at a much higher level than the street. The entrance of the building was decorated with a porch that supported an architrave with an inscription. Fragments of the inscription have been found opposite the temple, and (reused) on the intersection of the Decumanus and Via della Foce. They can now be seen on the street, opposite the temple. The distance between the columns of the porch can be deduced from the places of attachment on the bottom of the architrave, and is identical to the width of the main entrance of the building.

DIVO PIO [P]ERTINACI AV[G(usto)] COLLEG(ium) FABR(um) [TIGNV]AR(iorum) O[ST(iensium) CVRAM AGENTIBVS C(aio) PLOTIO CA[--,-] SALINATORE IANVARIO L(ucio) FAIANIO OLYMPO MAG(istris) Q(uin)Q(uennalibus) LVST(ri) X[XVIII]

The inscription is a dedication to the deified Pertinax and should be dated to 194 AD, that is to the reign of Septimius Severus. It reflects the dedication of the building and was set up by the guild of the builders of Ostia, the fabri tignuarii. The temple is therefore linked to the House of the Triclinia (I,XII,1), the guild seat of the builders. In that building a dedication to Mars was found, not surprising, because the builders were organized in a military way. The inscription of the Guild Temple points to the Imperial cult, but the temple may also have been dedicated to Mars. The attention paid by Pertinax to the harbours is documented by the ancient historian Dio: "While Pertinax was at the coast, investigating the grain supply ..." (Dio 74, 8, 2).

The words TIGNVAR OST were hacked away later. Fausto Zevi has suggested that this is the result of reuse as a threshold, but for that purpose the groove is much too wide. John Fabiano has suggested that in the fourth century the guild was renamed to collegium fabrum, after a reorganization to which a law from 329 AD would testify (Codex Theodosianus 14.8.1).

Behind the entrance of the building is a large hall. At the back of the hall are brick piers, supporting three masonry arches. Through the arches a courtyard is reached, with an altar in the front part and a temple on a podium in the back part. The floor and walls of the courtyard, the altar, and the podium of the temple were all decorated with marble.

In the lateral walls of the courtyard are square wall-niches at a height of c. 1.20: four at the west side, three at the east side (w. 1.30, d. 0.50). At the east side is also a semicircular floor-niche (w. 1.80, d. 1.00). The latter niche and the most north-western niche were certainly fountains, the others perhaps. A door in the north-west corner of the courtyard leads to some small rooms that were set against the west facade. Among these rooms is a staircase accessible from Via degli Augustali.

The temple was reached along a wide staircase. The pronaos and cella have disappeared. A fragment of a marble architrave was found, with a frieze of bucrania (skulls of an ox) and cult-vessels.

Through a door in the west wall of the podium two rooms below the temple could be reached (here the floor of the temple has largely disappeared). The rooms received light through six slit-windows, three in each lateral wall. In the south wall of the southern room, below the cella, is an apse.