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
History of Macedonia (ancient kingdom) of the Italian peninsula. In 216 BC, Philip V sent a hundred light warships into the Adriatic Sea to attack Illyria, a motion that did not go unnoticed by Rome when Scerdilaidas of the Ardiaean Kingdom appealed to the Romans for aid. Rome responded by sending ten heavy quinqueremes from Roman Sicily to patrol the Illyrian coasts, causing Philip V to reverse course and order his fleet to retreat, averting open conflict for the time being. In 215 BC, at the height of the Second Punic War with the Carthaginian Empire, Roman authorities intercepted a ship off the Calabrian coast