Detailed descriptions and interpretations of the Ostian storage buildings (horrea) were produced by Geoffrey Rickman (Roman Granaries and Store Buildings, Cambridge 1971), followed by a general study (The Corn Supply of Ancient Rome, Oxford 1981). Some warehouses can be identified through the presence of large storage-jars, or raised floors (suspensurae) meant to protect grain from damp and overheating. Lanciani reports that in the central-north part of the city "floors of the storehouses have been found still covered with a layer of grain which, on being brought into contact with the air, tumbled into dust" (Notes from Rome, 15 [1876]). In one case the name Horrea is recorded in an inscription in the facade (Horrea Epagathiana et Epaphroditiana). Other buildings can be identified as storage buildings on the basis of their resemblance to these buildings. A special category are the buildings with dolia defossa, huge, buried jars, in which wine or olive-oil was stored.
The storage buildings are all from the Imperial period, most of them from the first half of the second century, while some date back to the first century. There is a relation with the work of Trajan in Portus, possibly also with that of Claudius. As to the later history of the buildings: in one building a phase from the second half of the third century has been traced, and very few activities are documented in late antiquity. By now Portus was the main place for storage.
Characteristic for the appearance are buttressing, thick walls, few entrances, slit-windows high up in the outer walls, special locking devices, long rows of rooms (cellae), and ramps leading to the first floor. Rickman distinguishes two kinds of lay-out: cellae around a courtyard with portico or colonnade, and cellae along a corridor. The Horrea Epagathiana et Epaphroditiana have an axial lay-out, consisting of two vestibules, a courtyard, and an accentuated room. The axis was emphasized by the mosaic of the courtyard: behind the vestibule is a panel as wide as the vestibule with the depiction of a tiger, meant to be seen from the vestibule; behind is a large panel with meanders and a swastika; in front of the accentuated room is a panel as wide as the room with a depiction of a panther, meant to be seen from the room.
The size varies from quite small to very large. Most of the large horrea are, for obvious reasons, situated to the north of the Decumanus Maximus and Via della Foce, that is along the Tiber, and the main entrance of most of these is turned towards the river. Most of the smaller ones are to the south of the Decumanus and Via della Foce. Concentrations are found to the northwest of the Forum, and to the south of the eastern Decumanus. Storage buildings have also been identified in the Ostian Trastevere
Both the number and size of the storage buildings show, that they did not serve Ostia alone. They held reserves for Rome, even after the construction of Portus. Smaller horrea south of the Decumanus and Via della Foce, and perhaps others, served the local market. The Grandi Horrea were probably owned by the Emperor, and part of the grain stored there was taken to the bakery in the Caseggiato dei Molini, a bakery most likely working for the Emperor. Horrea I,VIII,3 were a non-Imperial investment, as is shown by an inscription in its facade: Horrea Epagathiana et Epaphroditiana, Epagathus and Epaphroditus being two freedmen. How many storage buildings were the property of the Emperor, and in which period, cannot be said.
The workers in the Imperial storage buildings must have been Imperial slaves and freedmen. As Rickman has remarked, "it is a remarkable fact that among the mass of Ostian inscriptions there is no reference to the workers and managers of horrea". Some data from outside Ostia is available however, largely from Rome, from Imperial horrea. Here slaves and freedmen only are documented, many of them Imperial. It is not known whether the workers in horrea usually lived in the building, or elsewhere.
The unloading of the ships and the transport of the goods to the horrea was not done manually only. In Rome cranes are documented called the "Kneeling Storks" (Ciconiae Nixae). The cranes could be set in motion through a connection with large wheels that were turned by people walking in them, a solution identical to the waterwheels for lifting ground water in baths.
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| Impression of the unloading of a ship. Misurare la Terra, Modena 1986, p. 167. | A kneeling stork. Photo: Wikimedia. |
One reason for the presence of many storage buildings in Ostia and Portus will have been the avoiding of a depency of the transport to Rome. And there may have been a second complication. Pliny the Younger, in a letter about a villa in Umbria, wrote: "The Tiber runs through the middle of the plain; it is navigable for ships, and all the grain is carried downstream to the city [Rome], at least in winter and spring. In summer the volume of water dwindles away, leaving but the name of a great river to the dried-up bed, but in the autumn it recovers its flood" (Medios ille agros secat navium patiens omnesque fruges devehit in urbem, hieme dumtaxat et vere; aestate summittitur immensique fluminis nomen arenti alveo deserit, autumno resumit) (Plinius, Epistulae 5,6,12, translation J.B. Firth). This might imply that goods could also not be taken from Ostia and Portus to Rome via the Tiber in summer and autumn. This was the mare apertum, when ships unloaded their cargoes in the harbour, and it would have been another reason for the presence of many horrea in the ports.