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 Persia of the dynasties in control of their empires in different historical periods: first were the Medians (Media Atropatene), then Parthians and finally Sassanians. In 64 BC Pompey conquered the remaining Seleucid territories in Syria, extinguishing their state and advancing the Roman eastern frontier to the Euphrates, where Romans met for the first time the territory of the Parthians. Mark Antony, in his quest to avenge the battle of Carrhae defeat, conquered in 33 BC some areas of Atropatene (northern Iran) and Armenia but soon lost it: that was the first time that Romans occupied a Persian territory, even if temporarily.