What is “a sally port” in castle defense?

The story behind the answer

Defenders used it to launch sudden sorties during a siege—slipping out to burn siege engines, ambush sappers, or seize supplies—then retreating before the attackers could respond. Because this was a potential weak point, it was kept small, discreet, and built with layered security: narrow passages, multiple locked doors, iron grilles, and even murder holes to stop any pursuers who found it.

The word “sally” comes from Old French saillie, meaning a sudden rush out. Many castles placed these concealed exits near the curtain wall or moat and disguised them within masonry or vegetation. Their purpose highlights a key truth of medieval warfare: strongholds weren’t only about holding out—they relied on active, targeted counterattacks to keep besiegers off balance.