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
Campaign history of the Roman military was the costliest Rome had suffered since the Battle of Cannae. After the Cimbri inadvertently granted the Romans a reprieve by diverting to plunder Iberia, Rome was given the opportunity to carefully prepare for and successfully meet the Cimbri and Teutons in the Battle of Aquae Sextiae (102 BC) and the Battle of Vercellae (101 BC) where both tribes were virtually annihilated, ending the threat. The extensive campaigning abroad by Rome, and the rewarding of soldiers with plunder from those campaigns, led to the trend of soldiers becoming increasingly loyal to their commanders rather than to the state, and a