One of the greatest consequences of Rome's expansion across the Mediterranean world in the course of the Republic and the earliest years of the Empire was an exponential growth in the population and extent of the city itself. The emperors of the first three centuries ad faced major strategic challenges in ensuring a regular annual supply of food to the city, as well as other goods. This volume brings together various contributions, to assess how far Portus, as the maritime port of Imperial Rome from the mid-first century ad, was the principal conduit for supplying Rome and the extent to which the commercial links that fed Portus were part of a single overarching network or a series of interlinked networks that extended across the Mediterranean. The volume begins with a detailed reconsideration of Portus and its relationship to Ostia and Rome, which is complemented by studies considering aspects of the commercial roles of Portus and Ostia, and of transport up the Tiber to Rome. It continues with studies that deal with a range of broader issues concerning the relationship of Mediterranean ports to Rome, Portus and Ostia, routes of commerce, and the archaeological evidence for commercial activity at a selection of ports (in Italy, Sicily, Hispaniae, Africa and the East); before returning to more general considerations of connectivity, networks, coastal geo-archaeology and computational methods.