Sasanian defense lines

The defense lines of the Sasanians were part of their military strategy and tactics. They were networks of fortifications, walls, and/or ditches built opposite the territory of the enemies. These defense lines are known from tradition and archaeological evidence.

The fortress systems of the Western, Arabian, and Central Asian fronts were of both defensive and offensive functions.

Mesopotamia

The rivers Euphrates, Great Zab, and Little Zab acted as natural defenses for Mesopotamia (Asoristan). Sasanian development of irrigation systems in Mesopotamia further acted as water defense lines, notably the criss-crossing trunk canals in Khuzestan and the northern extension of the Nahrawan Canal, known as the Cut of Khusrau, which made the Sasanian capital Ctesiphon virtually impregnable in the late Sasanian period.

In the early period of the Sasanian Empire, a number of buffer states existed between Persia and the Roman Empire, which played a major role in Roman-Persian relations. Both empires gradually absorbed these states, and replaced them by an organized defense system run by the central government and based on a line of fortifications (the limes) and the fortified frontier cities, such as Dara, Nisibis (Nusaybin), Amida, Singara, Hatra, Edessa, Bezabde, Circesium, Rhesaina (Theodosiopolis), Sergiopolis (Resafa), Callinicum (Raqqa), Dura-Europos, Zenobia (Halabiye), Sura, Theodosiopolis (Erzurum), Sisauranon, etc.

According to R. N. Frye, the expansion of the Persian defensive system by Shapur II (r. 309–379) was probably in imitation of Diocletian's construction of the limes of the Syrian and Mesopotamian frontiers of the Roman Empire over the previous decades. The defense line was in the edge of the cultivated land facing the Syrian Desert.