Depictions
A limited number of depictions is quite popular on the square. First of all fishes and dolphins. Merchant sailing ships are very frequent. The bow may be concave or curved. The stern is often shaped in the form of the head of a swan or goose, and has two rudders. Mainsail and foresail (artemon) can be recognized easily, together with the ropes of the rigging. The lighthouse of Portus, built by Claudius and repaired by Antoninus Pius, was also popular. A harbour scene is found in one back room only (statio 22) and therefore indicates a special situation.
Grain measures, round or cylindrical containers of wood, are frequent. The grain measures on the square are often called modii, but they were not: a grain measure was filled with an unknown number of modii, a capacity measure of ca. 8.6-8.7 litres. Accompanying the grain measure may be a rutellum, a bar, probably made of metal, with which the grain was leveled.[1] Finally, some wild animals are depicted.
Geometric designs
Floors with geometric designs are found both in front rooms and back rooms. They may fill the entire room, or half the room. They attract much less attention than animals and objects. We will therefore find them in waiting areas, meeting areas with masonry benches or wooden furniture, and in a corridor (statio 6). We will have to look for a different explanation however, when a geometric design surrounds depictions (statio 3).
Inscriptions
Two kinds of mosaic inscriptions are found on the square. First of all single-letter abbreviations, such as SNFCC (statio 34). They have no parallels. They will be treated at length separately, in the section "The auxiliary grain fleet of Commodus". Then there are many inscriptions that are very wide (several metres) and high, almost always in the back part of the front room. Many of these are inside a tabula ansata, many others are not framed.
Sometimes there is no mosaic text at all, leading us to think that there was an inscription elsewhere in the statio. The slender brick columns flanking the entrance are not suited. Rather we may think of marble inscriptions over the entrances.
Colours
All mosaics are black-and-white.[2] The mosaicists stuck to what was customary: a white background with black objects and animals. This sometimes leads to a discrepancy that is, however, easily accepted by the viewer. It makes no sense to depict a white night sky with a black lighthouse having a black fire burning on top. Still, that is how it was done, not in the least because swapping the colours would have had curious implications for the rest of the mosaic: a white text on a black background in a tabula ansata with a white outline; a white dolphin in a black sea (shades of grey were not created). In a few cases the mosaicist decided not to use this colour convention, which obviously needs an explanation: a white fire on top of the lighthouse (statio 22), a white grain measure (statio 55).
Accuracy
The dolphins are depicted in the way the Romans usually depicted them, partially as fantasy animals.[3] Ships, especially their rigging, are depicted in some, but not minute detail. The lighthouse was depicted with many variations, even though an accurate representation would have been easy: it was only five kilometres to the north-west of the square, approximately 120 metres high, and could easily be seen from Ostia.
Orientation
The orientation of the mosaics is yet another feature to be explained. Most mosaics should be looked at from the direction of the square. Sometimes depictions have been turned 180 degrees, or even 90 degrees. An easy way of solving this is by thinking of entrances and exits. In this context attention should also be paid to the joining of stationes: similarities between mosaics sometimes indicate that neighbouring stationes were used by the same group of people. Most intriguing are depictions with a different orientation that are so close to each other that they cannot indicate an entrance and exit (see statio 33).
Symmetry and axiality
As Clarke has pointed out, the front room often has an axis that is perpendicular to the axis of the portico. Heraldic depictions of dolphins and ships flank the axis, while a single object is on the axis, such as the arrow-shaped lighthouse and a grain measure. In this way the visitor is informed about the lay-out of the statio, about the front room and back room.
Symmetry and axiality are often used to draw attention in a counterintuitive way. This is achieved by placing texts and depictions slightly off-axis. It alerts the visitor, by implying that something is special, different from what is normal. Once alerted, visitors will be inclined not to walk across the text, but around it, reading the text with extra attention. In one case the asymmetry is even exaggerated, by omitting the left ansa of the tabula ansata (statio 12). As we will see, this leads to a flow in the interpretation, in combination with a dolphin swimming right through a frame. In statio 11 only two seasons are depicted, instead of the usual four. This may also be called asymmetry.
Barriers
In the back part of the front room may be wide and high inscriptions. Those in a tabula ansata immediately attract the attention of the viewer. They also form a visual barrier, alerting the visitor that access to the back room is restricted or not allowed. Those without a frame are much more transparent and do not attract attention as strongly. I have not found a reason for the applying or omitting of the tabula ansata. In one statio the text is in the middle of a marine / harbour scene (statio 23).
After crossing the barrier, the visitor will often find himself in a back room that is divided in a front and back half by a black band. The front half, usually with a simple white floor, seems to 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. 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 (all these remains are lost). The passage between the front room and back room may also be articulated by panels with depictions, covering both the back part of the floor of the front room and the front part of the floor of the back room.
Contrast and ambiguity
A simple contrast is that between a ship with raised sails and a ship with lowered sails: the first points to the transport across the sea, the second to the safety of the harbour. There must have been a good reason for the juxtaposition of two grain measures, one with and one without a rutellum (statio 38). Orientation can also lead to a contrast, when two objects with a different orientation are close together (see for example statio 35).
We might call ambiguity a special kind of contrast. We will find grain measures, the lower part of which is not a grain measure at all (stationes 33 and 34), and a tower that at first sight must be the lighthouse, but on closer inspection turns out to be a different kind of tower (statio 32). In one statio the word turris (tower) seems to be used with two meanings (statio 19).
Metaphors
Depictions taken from the traditional figurative, mythological repertoire are rare. In statio 10 an astrological sign was depicted. In statio 11 we have two tondos with the heads of two seasons, and an amorino riding a dolphin. In stationes 49 and 50 is a Nereid. We will have to ask ourselves why these depictions, metaphors, were preferred over real objects and real creatures in the harbours and on the sea.
Amount and selection of information
The inscriptions inform us that many stationes were used by shippers related to cities, either restricting their activies to the ports of these cities, exporting the produce from the hinterland of that city, or using these ports as a base for a wider area. The cities are located in Egypt, Africa Proconsularis, Sardinia, and Gallia Narbonensis. The depictions provide additional information, also by being omitted: a man at work with a grain measure without any marine depiction points to work with grain in the harbours, not to the transport of grain overseas or on the Tiber (statio 5).
The amount of information provided by the mosaics varies. We have already seen that sometimes there is no text on the floor, and I hypothesize that in these cases marble inscriptions over the entrances were used. A mosaic depiction may also be restricted to one or two dolphins, or a single grain measure. In these cases the information that is provided is symbolic, detached somewhat from the daily reality of shipping and trading. I suggest that rooms with minimal information on the floor were offices used by the Imperial administration, by representatives of provinces, and by large guilds relying on the services of other guilds.
Commodities
The square was used for organizing the Imperial food supply (annona) of Rome. The main commodity documented is grain, with olive oil coming in second place. I will argue that wild animals, fish and fish sauce, marble and perhaps metal may be added.
Crafts and professions
A profession documented very well by the inscriptions is that of shipper, navicularius. Most of them are found in the north half of the east porticus. One guild is documented in the north porticus.
The stationes in the south half of the east porticus were used by guilds that were active in and provided material for ship building and maintenance (wood shippers, navicularii lignarii; caulkers and sailmakers, stuppatores; rope makers, restiones; leather-workers, pelliones), construction work in the harbours plus the functioning of the lighthouse (shippers from Terracina, navicularii Tarricinenses), and the control of storage (grain measurers, mensores frumentarii). These guilds worked for or together with the guilds of builders and ship builders (fabri tignuarii and fabri navales). Porters (saccarii) are documented in a statio on the north side, the operators of the tow boats on the Tiber (codicarii) on the west side.
There is a striking absence of texts in the west porticus. Here too the mosaics regularly provide little information. It leads me to the hypothesis that especially this side of the square was used by larger groups of shippers (from provinces), and by different kinds of officials (superintendents, curatores; weigh masters, sacomarii; members of the staff of the procurator annonae). Messengers (frumentarii) are also documented on the square. Most likely they had been assigned with the practical aspects of the reorganization of the square.
(1) On grain measures see Jouanique 1969 and Minaud 2004.
(2) Only the depiction of a hunter in statio 52 has a few coloured tesserae of glass paste.
(3) In reality male dolphins are bigger than female dolphins, but visual differences are subtle. Pliny the Elder wrote about dolphins, about human beings who have been beloved by dolphins (also in Puteoli and Hippo Diarrhytus), about places where dolphins help men to fish (in Nemausus, Gallia Narbonensis), and about other wonderful things relating to dolphins (Naturalis Historia 9,7-10).