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
Potenza at present, some south of today's Potenza. The Lucani of Potentia sided against Rome's enemies during the latter's wars against the Samnites and the Bruttii. Subjugated during the 4th century BC (later gaining the status of "municipium"), the Potentini rebelled after the Roman defeat at Cannae in 216 BC. However, the Battle of the Metaurus marked the end of any Carthaginian aspirations in Italy and Potentia was reconquered by the Romans and reduced to the status of military colony. In the 6th century, the city passed to the Lombard Duchy of Benevento. Incursions by Saracens raiders menaced the city until