The mosaics on the square have often been described with disdain, as examples of disappointing, Severan art. They would be mere advertisements or billboards, static and boring, without any aesthetic value. They would contain many errors, and testify to lack of knowledge and understanding of the maritime world on the side of the mosaicists. Nothing could be further from the truth. It is true that the mosaics do not stand out because of their beauty, but we should not compare apples to oranges, or Rembrandt to Picasso. The mosaics are an intriguing form of communication.
The people working in the offices and the mosaicists working for them addressed the visitors in a great variety of ways, by employing a wide range of visual effects. Axiality and symmetry were achieved by heraldic depictions of ships and dolphins flanking a grain measure or the lighthouse, and by placing wide inscriptions in front of back rooms. Often however the rigidity was modified or broken, for example by placing an inscription or depiction off-axis, or by showing a ship with raised sails and water opposite a ship with lowered sails without water. The effect could be intensified, for example by omitting the left ansa of a tabula ansata, or by having a dolphin swim right through a frame. Stark contrasts were created: a grain measure is accompanied by an upside down amphora, a positive and swimming dolphin is next to a negative dolphin that is not swimming, a grain measure with rutellum is next to one without that implement. Colour effects were achieved by unexpectedly showing a grain measure as completely white, or by unexpectedly making the fire of the lighthouse white. Ambiguity was introduced, by changing the lower part of a grain measure into a room with a wide entrance. Little technical puzzels were added, such as a machine resting on a tower, and the way in which the light was emitted by the lighthouse. In one office the mosaicist even seems to place us inside the lighthouse, where we become aware of the damp interior, the thickness of the walls, and the height of the enormous tower above us. Metaphors were used: personifications of the seasons in a tondo, an amorino riding a dolphin, Nereids on a sea creature, a tree or a cargo as pars pro toto for a province.
It could well be that the choice of the effects was triggered by the auxiliary grain fleet, even if not applicable in a statio. The mosaicists had to find a way to refer to a paper fleet, a reality that might never materialize. Their approach may have been the inspiration for similar visual effects all over the square.
It is quite possible that some of the mosaics show a sense of humour. In the office of Narbo Martius a tower was depicted that at first sight seems to be the lighthouse of Portus, which is why every archaeologist describing it begins by explaining that it is not the lighthouse. Only on closer inspection does it become obvious that it had a different function. But such images were not meaningless visual games. Landlubbers could solve a puzzle of the fire of the lighthouse, but it would probably result in no more than the satisfaction of having solved it. When people in the shipping business did so, it was a different matter. They would immediately be aware of the importance of a lighthouse and a safe harbour, remembering storms, jettison, and shipwreck. They would realize that those working in the office were also more than familiar with these dangers, so that a bond was created between these people. They shared the same fears and deep appreciation for a lighthouse and a harbour. Recognizing a machine led to a similar kind of bond, based on shared knowledge.
Special effects were also used to elucidate the modus operandi inside the statio. Heraldic ships and dolphins, and the arrow-shaped lighthouse function like direction signs leading to the back rooms. By placing texts and depictions slightly off-axis the visitor was invited to study them. The wide, beam-shaped texts just in front of the back rooms created something of a barrier between front room and back room, and prevented a headlong dash through the office to the back room. After crossing the barrier, the visitor would often find himself in a back room that was divided in a front and back half by a black band. The front half, usually with a simple white floor, could have functioned as a waiting area. This in turn suggests that the back half of the back room was of special significance, a meeting area one would think. According to old plans, a bench was sometimes set against the back wall or in a U-shape in the back half of the back room.
The people involved are depicted in only a few stationes. In the office of the grain weighers a man is kneeling next to a grain measure, in the office of the porters a man is seen carrying an amphora. We see such men posing on a well-known mosaic in the Aula dei Mensores, a building used by the grain measurers. The measurers are joined by a porter and face the viewer, proudly displaying their activity.
Mosaic of grain measurers in the Aula dei Mensores (I,XIX,1.3).
Photo: SO IV, Tav. 188.Mosaics with similar effects may already have been made in Rome, but still we must ask ourselves who came up with the idea to use all these special effects on this square in Ostia. Here it is important to stress that the square was of eminent importance, linked as it was to the supplying of Rome. One thing is certain: this visual approach was approved by the Imperial administration, first the procurator of the food supply (annona), who will have talked to the prefect of the food supply, who in turn talked to the Emperor. Perhaps the artists came up with the idea, in discussions with the skippers and traders. But treating the supplying of Rome in this remarkable way would have been a brave initiative. It is conceivable that the idea came from Commodus himself, talking with the mosaicists. Commodus used a villa at modern Tor Paterno, a bit to the south of Ostia, and he will surely have visited Ostia and Portus on a number of occasions. Remarkable artistic developments are documented in the late-Antonine and early-Severan period, such as the introduction in painting of the so-called linear style or catacomb style, with a white background and slightly inclinated bands, and the portraits of Caracalla, breaking with tradition, characterized by a deep, downward frown on the forehead. To such new approaches the mosaics on the square may be added.
