The building was, of course, not a domus. The plan of the ground floor is well-known in Ostia. A central light source is flanked by a major accentuated room (25) on one end, and a minor accentuated room (30) on the other. One of the long sides is taken up by a row of small rooms. The vestibule (3) is unobtrusive. This is the typical plan of a medianum-apartment. In this case the medianum is a courtyard: it could not receive light through windows, because of the row of shops to the west, and the courtyard is also the major source of light for the upper floors. So at first sight we might think that the ground floor contained a single, rented apartment. There are however too many anomalies:

• The large latrine does not belong in a rented apartment.
• The same can be said about the three additional entrances to the building, from rooms 5, 7 and 12, and it is most curious that the minor accentuated room (30) could be reached from the back-room of a shop.
• In the medianum-apartments there are no parallels for specific, permanent features such as the terracotta relief in the courtyard.
• The relief is reminiscent of the many shop-signs that have been found in Ostia.
• The ground floor was not the obvious main floor of the building: corridor 27 to the west of the courtyard serves no purpose; it is only there, because it was repeated on the upper floors, where it was functional.
• The three niches in the north wall of the courtyard, on the first floor, suggest that the first floor was of considerable importance, a view that is supported by the quality of paintings from the upper floors, that can now be seen in shop 8.
• Shop 4 is wider than shop 6. Perhaps this was done to make the addition of a window in back-room 5 possible. Why this great desire to take (indirect) light to room 30?

As long as the final publication of the recent research by Marinucci has not appeared it is pointless to pursue issues such as the absence of floors in the later phases that Marinucci identifies, or the curious situation in room 25 (Marinucci: 27 / 28), where part of the opus sectile seems to be in a small room, and where there is no clear alignment of the opus sectile and the main entrance to the room. But it is clear that his research has added at least one more anomaly:

• The marble fountain in the courtyard covers c. one-third of the surface of the courtyard, an abnormal ratio.

The clear traces of fire in room 26, combined with Calza's statement that the building was not destroyed by fire, suggest that during its existence part of the building was damaged by fire, and rebuilt. This might explain the reinforcing masonry, all of which is found in the west part of the building.

The basalt blocks and trough in rooms 20 and 30 may indicate that the ground floor was in later antiquity used as stable by a nearby bakery, such as the Caseggiato dei Molini to the east, or the Caseggiato del Balcone Ligneo to the south. There is, on the other hand, no obvious explanation for the large reservoir in the courtyard (of a type that is typically found on streets and squares) and the low basin to the south (note that the courtyard was not paved with basalt blocks).

During my research on private religion in Ostia I noted that the compitum (a shrine at crossroads) on Piazza dei Lari is - as far as can be judged from the plans in Scavi di Ostia I - exactly opposite the centre of the House of Diana. The compitum consists of a basin, a round altar, and a rectangular room with wide openings (most of which were later blocked). On the altar are depictions of the Lares Compitales, Panes belonging to the train of Dionysus, and Hercules. The masonry is yellow opus latericium, and according to Heres it is Antonine, like the masonry of the House of Diana. This seems to have been one of the main compita of Ostia, together with an old shrine on the Bivio del Castrum. I would like to forward the hypothesis that the ground floor of the building was the seat of the officials of the cult at the crossroads, freedmen and slaves called magistri et ministri vici. Becatti has stressed that a few inscriptions from the building are related to a guild. One of these mentions a seat (schola), installed with the involvement of freedmen of Trajan (Marci Ulpii). From the building comes a painting referring to one of the popularia sacra. In Portus people living in certain districts could form a so-called spira and worship specific deities. The Bonadienses worshipped Liber Pater (Dionysus; CIL XIV S, 4328), the Traianenses Dionysus and Diana (IG XIV, 925 and the difficult inscription DIANA IOBENS IVB TRAIANENSIVM, Thylander B287). A painting from Ostia, now in the Vatican Museums, shows Diana on a pedestal, in a structure that is reminiscent of a compitum. The painting is described in detail elsewhere on this website. Note that the Tempio di Ercole is very close to the Bivio del Castrum, and note that an altar mentioning Hercules was reused in the mithraeum in the building. Note the clustering of rural deities in this part of Ostia (Diana, Silvanus, Ceres, Liber Pater). Cf. the Arch of Trajan at Beneventum, and cf. the Augustan poet Grattius, Cynegetica 13-20: "The life that was imperilled by warfare against wild beasts, where most it needed help, thou, Diana, didst deign to shield with aids of thy discovery, and to free the world from harm so great. Under thy name the goddesses joined to them a hundred comrades: all the nymphs of the groves, all the Naiads dripping from the springs, and Latium's satyrs and the Faun-god came in support; Pan, too, the youth of the Arcadian mount, and the Idaean mother, Cybele, who tames the lions, and Silvanus rejoicing in the wilding bough" (translation Loeb, Minor Latin Poets). See also Bakker 1994, 69, 199, 202 n. 39. There is no hard evidence for the hypothesis, and it does not offer a simple explanation for the anomalies in the building. It could explain the contrast between simple and monumental features, and it makes the large latrine understandable as a service to the district. The open character of the building may be a confirmation that the magistri et ministri also had to perform non-religious duties (Bakker 1994, 203).

Plan of the district. From SO I.