Citadel

It is short story book. A citadel is a fortress protecting a town, sometimes incorporating a castle. The term derives from the same Latin root as the word 'city', civis, meaning citizen. In a fortification with bastions, the citadel is the strongest part of the system, sometimes well inside the outer walls and bastions, but often forming part of the outer wall for the sake of economy. It is positioned to be the last line of defence, should the enemy breach the other components of the fortification system. A citadel is also a term of the third part of a medieval castle, with higher walls than the rest. It was to be the last line of defence before the keep itself.