Dumbarton Oaks Research Library and Collection: Washington, D.C., in three volumes as number 39 in the series (2002)
The principle that the active and coordinated collaboration of nature and man is an essential requirement for the creation of a network of communications is of fundamental importance. Furthermore, when the objective is the construction of roads, people usually revert to the alignments and routes of the past. The Byzantines inherited and used the well-organized system of Roman roads dating from earlier times, adapting it to the requirements of their own period. They also lived, fought, and traded at sea— a natural extension of the land and an element of cohesion in the empire. In the days of its greatest glory, the Byzantine Empire unified and administered vast tracts of land linked by sea. Constantinople, in its geographic position, was a further expression of this duality of land and sea.
The city stood close to the strategically vital axis that linked Europe and Asia—the valley of the Danube with that of the Euphrates—and at the point where that major diagonal land route intersected with the Mediterranean/ Black Sea marine axis. Its position was thus decisive for the directions and routes of communications by road and water. Whoever was master of Thrace and the roads that led to the capital could control the flow of supplies to it overland, but in order to starve the city into surrender one would also have to control communications by sea.