The Castle of Agios Georgios was built on a hill 7 km from Argostoli and dominates the southern part of Kefalonia and the bay of Argostoli. The first houses outside the archaeological site began to be built in the previous century, when the area was recognized and protected as an attraction, but also an important historical monument.
The fortress has an area of about 16,000 square meters and a perimeter of 600 meters. It has a polygonal shape. It consists of the outer wall, the inner enclosure, which has the shape of a horseshoe, and a rocky peak that rises in the center of the enclosure where the ruins of the so-called Old Fortress are located. Churches and buildings are preserved inside, as well as in the suburb (borgo) east of the entrance. In the borgo of the Castle there is the metropolitan church of the Holy Church of Evangelistria, a typical example of Ionian Baroque. Inside are kept remarkable post-Byzantine icons from the ruined temples of the Castle. To the south of the Castle is the historic Monastery of Agios Andreas of Milapidia. In its old katholikon there is a ecclesiastical museum with remarkable icons. In the courtyard of the fortress, near a small square, one will also see the ruins of the Catholic church of Agios Nikolaos. Inside the castle there was a multitude of churches, the ruins of which are preserved today. [
Its creation dates back to the twelfth century AD by the Byzantines. During the rule of the island by the palatine counts Orsini, some changes were made, which were generalized in the middle of the 16th century, when it was in the hands of the Venetians. The Venetian fortress was built on the ruins of the Byzantine one by the engineer Nikolaos Tsimaras in 1504.Its walls with three bastions are preserved in very good condition until today.The most important moment of its history was its siege and fall at Christmas 1500 by the united Christian forces of Venetians and Spaniards, under the general leadership of Gonzalo de Córdoba, from the hands of the Ottomans who had occupied the island in 1484. With the demographic recovery of the island, the dwellings inside the fortress reserved for the authorities and the nobles (borgo) increased, and gradually a settlement (exombourgo, suburb) developed around and under the walls.
The southwestern part of the wall was weaker equipped. The armor of the fortress on this side was natural, because the terrain is rough, rocky and steep, so that it does not lend itself to attack and deployment of the infantry by the standards of that time. Inside the fortress there were public and private buildings, temples, food and ammunition depots, barracks, hospitals, prisons, water tanks. There is also information that on many buildings were built-in coats of arms of nobles.
The fortress of Agios Georgios lost its defensive importance from the end of the 16th century. The defense of the island now required the construction of forts near the seas and ports. The castle was damaged by earthquakes in 1636 and 1637. Although the settlement of nearby Argostoli in time surpassed the Castle in economic and social importance, Kastro continued to be the capital of the island until 1757. Only then was the headquarters of the authorities moved to Argostoli.