Three kilometers NW of Asprovalta in the Prefecture of Thessaloniki, at the top of an imposing granite rock of Mount Kerdylio, are the ruins of a medieval castle.
It is probably a Byzantine fortress.

The steep rock has the name “Rock of Saint George” or “Plaka of Saint George” or “Rock Monastery of Stefanina”.
Near the castle, a little lower, is the Monastery of Agios Georgios which gave its name to the rock.

Structure, Fortification & Buildings

The total perimeter of the fort is estimated to have been around 400m, of which only 60m were walled. It is a Γ-shaped rampart on the northwest side of the rock, which was also the only possible access point to the castle, through the neck formed between the rock and the area of the Monastery of Agios Georgios.
The rest of the rock is unfortified, as it has natural protection from the steep vertical rocks. Most of the wall and buildings of the fort have collapsed and have been covered by dense vegetation.

The construction of the wall on the NW side consists of semi-processed stones with connecting mortar between them.
Following the path that leads to the castle and reaching the wall, we notice to the right of the entrance the best preserved part of the wall with a maximum height of 3.5m and a thickness of 2 m, which after 15m makes a right angle (shape Γ) and continues for another 20m, with a maximum height of 2m and a thickness of about 1.5m. To the left of the entrance, one can see the remains of a wall with a length of 20 meters at a small height. The gate was probably where the current entrance to the rock is located.

To the right of the entrance, there are the remains of an unknown oblong building attached to the inner side of the wall, separated longitudinally into two main parts. The remains of a rectangular building with dimensions of 2.4✖2.0 meters can also be found. It was probably a small church.
Inside. after the wall, there are scattered ceramics.

At the highest point (463m.), located in the southeastern part of the rock, there are remains of buildings covered by vegetation.
So this was not an impromptu fortification, but a normal castle, with buildings, a church and traces of a settlement.
The location is excellent, with the possibility of supervision over the entire Strymon gulf but also the coastal-plain zone of Asprovalta through which the ancient Egnatia road passed. There was also visual contact with neighboring castles in the area, such as the castle of Leipsasda (Stageira), the Paleokastro of Stavros and Chrysopolis at the mouth of the Strymon.
Today there is a wooden gazebo at the top.

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