Krk is the only city in the Primorsko-Goranska Country which has a completely preserved city fortification system around its entire perimeter. It consists of a citadel, fortress walls, towers and other facilities built in different historical ages: the Hellenic period, the age of the Roman Republic and the early Roman Empire, Late Antiquity, the Middle Ages, and the Romanesque period (construction work during the Renaissance was limited mainly to alterations of already existing facilities).