Defence-in-depth (Roman military)

Defence-in-depth is the term used by American political analyst Edward Luttwak (born 1942) to describe his theory of the defensive strategy employed by the Late Roman army in the third and fourth centuries AD. Luttwak's Grand Strategy of the Roman Empire (1976) launched the thesis that in the third and early fourth centuries, the Imperial Roman army's defence strategy mutated from "forward defence" (or "preclusive defence") during the Principate era (30 BC-AD 284) to "defence-in-depth" in the fourth century. "Forward-" or "preclusive" defence aimed to neutralise external threats before they breached the Roman borders: the barbarian regions neighbouring the borders were envisaged as the theatres of operations.

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