Citadel

A citadel is the fortified area of a town or city. It may be a castle, fortress, or fortified center. The term is a diminutive of city, meaning "little city", because it is a smaller part of the city of which it is the defensive core.

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. The functions of the police and the army, as well as the army barracks were developed in the citadel.