How do Barbican defend the castle?

The Barbican defends a castle by serving as an advanced fortification that acts as a first line of defense against attackers. Typically featuring a gatehouse and protective walls, it often includes features such as arrow slits and murder holes to repel intruders. The structure is strategically designed to funnel enemies into kill zones, making it easier for defenders to target them. Overall, the Barbican enhances the castle's security by creating a layered defense system.