It was built during the reign of Justinian at the ancient citadel of Patras. At times it was conquered by the Franks, Constantinos Paleologos, the Venetians and the Turks and underwent to building interventions. The Patras Castle was built during the second half of the 6th century century upon the ruins of the ancient Acropolis. In 805 AD the inhabitants of the city were besieged by Slavs and Saracens and their victory, a miracle of the city's patron Saint Andrew, was important for repelling the barbarian invasions in Peloponnese. Until World War II, it remained in continuous use for the defense of the city as an administrative and military center. The castle consists of a triangular outer enclosure reinforced with towers and ramparts, which were originally protected by a deep moat and an inner enclosure rising in NE angle and protected by a moat. The building today shows the evidence of the work done by each of its conquerors to repair and adjust to the development of military technology. The original building is now visible mainly in the northern wall, its traces however, exist on all three sides of the walls, indicating that the original Byzantine fortification was about the same perimeter. The castle consists of two parts: a) The broad triangular outer enclosure with towers and bastions, which included the three sides of the deep trench, and b) the inner enclosure rising on the NE corner of the castle, a natural mound. The inner fortification comprised six towers-bastions around (and therefore called exapyrgio) a water tank and buildings in its interior.