This book proposes a new approach to the Hellenistic and Roman harbours of the Aegean, based on the combined study of harbours and contemporary ships, seamanship, and commerce. It focuses on the capacity of harbours to accommodate and serve certain numbers of ships, their cargo, their crews, and their passengers. This is achieved through the study of a variety of archaeological, written, and geomorphological data on harbour configuration, and subsequent analysis relating these harbours with the ships that were most likely to use them. Two harbours are used as cases studies, the important commercial centres of Delos and Kenchreai. The results reached concerning these harbours are then discussed in a wider perspective and contextualized with other contemporary sites in the Aegean, as well as within a wider scientific discussion over commerce and seamanship in the Hellenistic and Roman Mediterranean.