The Byzantine castle “Avret-Isar” or “Gynaikokastro” is built at the beginning of the 14th century, above the old Gynaikokastro. It was important to be built at that point, to supervise the valley of Kilkis, and the passage between the rivers Gallikos and Axios made it a very important bastion for centuries and for every civilization that passed its gates. It protected the inhabitants of the area and the city of Thessaloniki, 45 kilometers south, while it also served for the safe storage of the crop.
Its name came from two possible versions, one of which is related to the wife of a commander who had taken care of him and the other to a popular myth. . In any case, it was an important fortress, with an outer enclosure of walls of 614 meters, reinforced at intervals with rectangular and semicircular towers. The citadel was built internally, with a separate fortification and its two-story, square tower is today the best-preserved part of the castle.
The period of construction, in the place of an older fortification, is placed in 1328-1341, in the Byzantine period 1328-1341, by Andronikos the 3rd and from the first years of its foundation, it played an important role in the developments of the civil conflict in Byzantium, until its decline in the 17th century.