If the birth of the settlement of Ostia is closely tied to salt—its foundation as a colony was primarily aimed at controlling and exploiting the nearby salt pans at the mouth of the Tiber—it was certainly grain that became the key driver of the city’s development from the late Republican period through the entire Imperial age.
The demographic, economic, and urban growth of Ostia as Rome’s port is inextricably linked to the import of goods, both perishable and non-perishable, that reached the capital from across the provinces of the Empire via Mediterranean trade. Among these, grain was undoubtedly the most important: largely intended for the free distributions (frumentationes) guaranteed by the central government to Roman citizens, it was a fundamental component of the population’s well-being, and as such, a pillar of the State’s economic and political stability. To facilitate the unloading, transportation, and storage of grain, a public area in Ostia between the Decumanus and the Tiber was designated in the second half of the 2nd century BCE, as evidenced by the so-called “Cippi of Caninius,” preserved below the current street level of the Decumanus.
Grain was mainly imported from the western Mediterranean provinces—Sardinia, Sicily, Egypt, and North Africa. Personifications of some of these provinces are depicted in the so-called Mosaic of the Provinces, which decorated a room of the Baths on Via dei Vigili, built in the 1st century CE and later replaced by the grander Baths of Neptune.
Grain arrived in the ports of Ostia and, from the 1st century CE, in Portus, aboard large merchant ships that crossed the Mediterranean. From there, it was transshipped onto smaller riverboats (caudicariae), which traveled up the Tiber to dock at the river port of Ostia or continued on to Rome. These scenes are vividly illustrated in the Piazzale delle Corporazioni. Because the grain was typically transported in vegetable-fiber sacks, the perishable nature of the containers has left only faint archaeological traces, unlike the liquid and semi-liquid goods (like wine, oil, or garum) transported in durable amphorae and terracotta dolia.
The loading and unloading operations at the port docks or during transfers between ships were carried out by saccarii (porters), depicted in a series of terracotta statuettes found in Ostia. Wearing short tunics and round caps, the saccarii are shown carrying heavy grain sacks on their shoulders, with a simple but expressive style. In addition to these figurines, saccarii appear in a fresco depicting the ship Isis Geminiana, discovered in the necropolis on Via Laurentina and now housed in the Vatican Museums, and in the mosaic decorating the Aula of the Mensores, part of a larger building complex interpreted as the headquarters of the grain measurers’ guild (mensores frumentarii).
The close relationship between the measuring and storage of grain is evident in the architectural complex comprising the Building of the Grain Measurers and the nearby Granary at the Small Market, located in a central area behind the Forum and the Capitolium, adjacent to the river dock. Like most granaries in Ostia, these two buildings were situated between the Decumanus and the riverbank, to ensure quick and easy access from the Tiber. Other grain-storage facilities included the Grandi Horrea and the Horrea Antoniniani, identifiable by the unique construction of their cell floors, which were raised on brick pilasters to keep the grain ventilated and protected from ground moisture.
All transport, unloading, inspection, sorting, and storage activities were closely overseen by the officials of the Annona, the administrative body tasked with ensuring a steady flow of supplies from the provinces to Rome. This body was directed by the praefectus annonae, a magistrate of equestrian rank directly accountable to the emperor. Numerous epigraphic testimonies in Ostia attest to the presence of prefects and procurators of the Annona, who maintained a privileged relationship with the port city. They likely had offices and residences here, perhaps identifiable with some of the more luxurious late antique domus, such as the Domus of Fortuna Annonaria.
However, not all the grain stored in Ostia was destined for Rome. Evidence of smaller-scale depots and, more importantly, the presence of bakeries (pistrinae)—with attached ovens and shops—suggests that grain was also used locally. These bakeries handled milling, kneading, baking, and selling bread. One particularly well-preserved example is the Mill of Silvanus, located opposite the Grandi Horrea and directly connected to it. Another is the more remote Mill on the Semita dei Cippi.
The Route
The itinerary begins at the entrance, reaching the first of the so-called Cippi of Caninius, at the start of the Decumanus near the Piazzale della Vittoria, then continues to Via dei Vigili, a side street of the Decumanus that borders the Baths of Neptune, from which the Mosaic of the Provinces can be viewed.
It then follows the Decumanus to the Theatre, and crossing through it, reaches the Piazzale delle Corporazioni, whose mosaics vividly depict grain transport, transshipment, and measurement.
Returning to the Decumanus, a short walk leads to the Grandi Horrea and the nearby Mill of Silvanus. Back on the Decumanus, the route continues to the Forum, and skirting the left side of the Capitolium, leads to the southern entrance of the Small Market. After crossing this space, visitors arrive at the Building of the Grain Measurers, and turning left, they enter the adjacent granary, located at the corner between the Small Market and the Horrea Epagathiana. Exiting here, a left turn onto Via degli Horrea Epagathiana leads to its end, where a right turn onto Via della Foce brings visitors to the Aula, Temple, and Horrea of the Mensores.
From here, retrace Via della Foce back to the Decumanus, following it toward the forum area. Beyond the eastern gate of the castrum, a detour south leads to the Mill of the Semita dei Cippi, one of the best-preserved in the city. After crossing the building, head north along the eponymous road, then turn east onto Via della Fortuna Annonaria to visit the Domus of Fortuna Annonaria. After the visit, return to the Decumanus to exit the site.