Forts and megafortresses, natural and artifcial barriers: the grand strategy of the Sasanian Empire

The 2014 field season of the joint project, between the ICHHTO and the University of Edinburgh, has yielded fascinating new insights into the defensive strategy employed by the Sasanian Empire. It has long been recognised that this vast empire used natural barriers, such as the Caucasus, as defensive obstacles. More recently, much more evidence has emerged for the skilful use of artificial barriers to close gaps between natural obstacles, on a scale not seen in the Near East before or since. James Howard Johnston has persuasively argued that rivers and canals were used, inter alia, for defence in Sasanian Mesopotamia, and the same appears to be true in the Gorgan Plain. A canal leading along the Great Wall of Gorgan made any hostile crossing far more difficult. Our latest research suggests that two successive reservoirs were created to close a gap in the Great Wall. Whilst forts with permanent garrisons guarded the Gorgan Wall, installations of far greater magnitude were built in the hinterland. The largest of these, Qal’eh Pol Gonbade Kavus, of c. 125 hectares size, is similar in dimensions and design to Qal’eh Gabri near Varamin and Torpakh Kala in the hinterland of the Sasanian Derbent Wall. These megafortresses, far larger than any in the contemporary late Roman world, were probably temporary bases for the field army. Whilst more fieldwork is needed to firmly date the foundation of Qal’eh Pol Gonbade Kavus, we succeeded in shedding light on its architecture and later reuse. It appears that the Sasanian Empire’s military success was based on a highly flexible, sophisticated and innovative use of its resources.