Defence in depth in order to retreat successfully, and they assume that the defender's morale will recover from the retreat. A possible early example of this came at the Battle of Cannae in 216 BC, when Hannibal employed this manoeuvre in order to encircle and destroy eight Roman legions, but that is disputed by some historians. Edward Luttwak used the term to describe his theory of the defensive strategy employed by the Late Roman army in the 3rd and 4th centuries AD. Later examples of defence in depth might be European hill forts and the development of concentric castles. In those examples, the
Romans in Sub-Saharan Africa in Africa south of the Equator has been discovered in the Graeco-Roman world or in contemporary Arabia, nor is there any mention of such an article in written records: while the coins are the only ancient European or Arabian articles that have been found in the southern parts of Africa. Additionally it must be noted that Emperor Augustus decided that the circumnavigation of Africa should also be attempted (in 1 BC). Romans had two naval outposts in the Atlantic coast of Africa: Sala Colonia near present Rabat and Mogador in southern Morocco (north of Agadir). The island of Mogador prospered