Defence in Depth [DiD]
The ancient theory of "Defence in Depth" is a military strategy that aims to delay rather than prevent the advance of an attacker. This approach involves the use of multiple 'layers' of defence that the attacker must breach to achieve their objective.
The Defence in Depth theory is still applied today, and involves a risk based assessment to design a multilayered and comprehensive approach to mitigate threats to people, property and information.