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
Ancient Celtic music The recital of "barbaric songs" is reported for a member of the Celtiberian infantry during the battle of Cannae in 216 BC, as he was attacked by the Roman consul. National songs are already attested by Tacitus for the Caledonians. Livius reports Gallic war songs that were heard at the river Allia. After the Gallic victory (ca. 387 BC) the city's inhabitants had to endure the dissonant battle chants. A sole Gallic warrior is reported to have gone into a fight singing. Livius on the other hand only describes the Roman Titus Manlius, who would defeat him in 361 BC,