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 maritime history and the Bay of Bengal. South Asia had multiple maritime trade routes which connected it to Southeast Asia, thereby making the control of one route resulting in maritime monopoly difficult. Indian connections to various Southeast Asian states buffered it from blockages on other routes. By making use of the maritime trade routes, bulk commodity trade became possible for the Romans in the 2nd century BC. A Roman trading vessel could span the Mediterranean in a month at one-sixtieth the cost of over-land routes. The Ancient Egyptians had knowledge of sail construction. The first warships of Ancient Egypt were constructed during