As you walk inland from the quay, you marvel at the huge, rectangular building before you, the Porticus Aemilia, whose construction is a tribute to Roman engineering and whose function represents the tremendous organizational skills that kept the city of Rome supplied with both luxuries and necessities. This vast structure, 533 x 98 yards, was originally constructed of wood by the consuls M. Aemilius Lepidus and M. Aemilius Paullus in 193 BCE (hence its name), and was rebuilt in concrete in 174 BCE, making it the oldest surviving concrete building in Rome. The roof is composed of 50 parallel barrel vaults supported on 294 internal pillars, as demonstrated in this city model, which shows the Porticus Aemilia in its context. This is the view of Rome that travelers sailing up the Tiber would see, with the Aventine hill rising up behind the Emporium and Porticus Aemilia.
Here you see the heart of the harbor's efficiency, a kind of customs office where goods can be inspected, measured, sorted and protected until they are transferred to more permanent storage in the warehouses and granaries. The thousands of people working in the harbor district are organized through a complex, interlocking system of imperial officials and commercial associations called guilds (collegia). The names of the guilds give some idea of the specialization involved in harbor work: codicarii (boatmen for the largest type of river barge), fabri navales (shipbuilders), restiones (ropemakers), saccarii (porters carrying grain sacks), phalangarii (porters carrying wine or oil amphorae), mensores frumentarii (measurers of grain), horrearii (warehouse workers), and custodiarii (warehouse guards), to mention just a few. There are also numerous guilds for the various types of merchants. See, for example, this mosaic from the Square of the Guilds in Ostia representing a ship and a grain measure; the inscription reads "navicul[arii] et negotiantes Karalitani" ("ship owners and merchants from Karales," modern Cagliari in Sardinia).
The quay itself reflects this organization and specialization, since different sections are marked off for different types of cargo. The part of the riverbank closest to the Porta Trigemina is called the Marmorata, where blocks of marble of every type and color are imported; the blocks are so heavy that they must be moved by large cranes (see a relief of a Roman crane and a reconstructed model). In the Portus Lignarius section timber is imported from Cyprus, Lebanon, andother parts of Italy, and to the east is a portico that was built specially for the timber-merchants long ago.
One large section is devoted to the importation of grain from the provinces of Egypt, Africa, and Sicily (this silver coin from Egypt, shows a grain ship leaving the harbor at Alexandria, and this wall painting from Ostia shows a riverboat being loaded with grain). Ensuring an adequate grain supply for the huge populace of Rome is one of the major preoccupations of the Emperor, since the state maintains a dole system (annona that provides about one-fourth of the adult male citizens of the city of Rome with a free monthly ration of grain. To learn more about the dole and see whether you might be eligible, walk back through the Porta Trigmemina to the Temple of Ceres, goddess of grain.
Thinking to yourself that you can't live by bread alone, you turn your eyes to the Portus Vinarius section of the quay, where imported wine is brought to Rome. You watch a porter unloading a wine amphora from a small service boat and follow him behind the Porticus Aemilia to one of Rome's most important warehouses, the Horrea Galbana, where two extremely important liquid commodities, wine and olive oil, are stored.
Horrea Galbana