The fortress of Christoupolis is very often cited in reference sources after the end of the 12th century and it successively came into the possession of Lombards (1204), Francs (1208), Byzantines once again, and after that of the Ottomans (1391). As all the Byzantine fortifications, the same applies in the case of the fortress of Kavala: it has exterior surrounding walls and a main citadel, the utmost defense section of every city.
The fortress constitutes an area with fortified surrounding walls, that follow the lie and slope of the ground while presenting a hypsometric difference of up to 10 metres and is divided into two parts by a traverse wall with direction from NW to SE.
The exterior surrounding walls, that fortify the lowest and most unsafe side of the hill, have an irregular form, an average length of 65 metres and width that varies from 17 metres in the S.W. side up to 70 metres on the opposite side. Two square towers (A and B) reinforce its walls (in the N.W. and N.E. corners respectively), in addition to a polygonal one, approximately in the middle of the Eastern curtain (part of a wall amongst two ramparts), as well as a bastion in the S.E. corner.
The internal enclosure encompasses the highest point of the peninsula, at about 70 metres above sea level, which is almost flat and naturally fortified from three sides. It has a regular form with dimensions of 90 by 37 metres. At the west end of its northern curtains, a polygonal outwards configuration of the walls is apparent, that we conventionally call the N.W. rampart, while at its western end a large area of about 12 by 8 metres is created, which also appears to exert outwards noticeably. The N.E. curtain, which at the same time also functions as partition wall of the two surrounding walls, is interrupted by a cylindrical tower as well as by a communication gate.
The internal enclosure constituted the most important part of the citadel, since it included all areas essential for its defense. These areas were: the water cistern at the East of the central circular tower, the ammunition and food storage house located in the building that is nowadays called a prison (fylaki); areas suitable for guards’ lodging, in the west end a construction (outpost) and probably and in other habitations, whose foundations began being revealed in relatively recent researches (1976), as well as a tower isolated from the curtains, suitable to put up one last defence attempt.
Typologically the citadel is placed among the medieval surrounding walls of the “white era”, the time that use of gunpowder had still not prevailed in the martial techniques applied. Consequently, the fortress was destined to resist attacks with the use of swords, bows and arrows, and not attacks from firearms of great destructive force. The lack of strong fortification is what characterises the construction of towers, entrances and walls.
The entire citadel is built with crude stones of local granite, mixed with bricks and marbles for secondary use, bonded together with plenty of lime mortar. The marble fragments are found specifically in the lintels and thresholds of the citadel’s gates as well as on the entrances of the central circular tower and the prison.
We are informed about the construction of new walls in the citadel’s castle, made by the Ottomans in April 1425, by a letter from the Venetian captain Pietro Zen towards his brother on the 23rd of July 1425 that is saved in the Cronaca Morozini code. It contains a detailed description of the attack that 10 Venetian galleons attempted against the castle of Christoupolis, as well as of its occupation by them.
The letter was published, after being translated by K. Mertzios: “… The occupation of this castle must have terrified the Turks to such an extent, more than any other war, for this castle lies in an important strategic position. It is the passage to Gallipoli, Andrianoupoli and to a part of Greece. For these reasons, the Admiral of our fleet noble Fantin Michael has decided to keep it under our possession and to fortify it, since it is highly useful to us. And indeed, the fortification commenced immediately both on the inside as well as the outside, where we constructed a stone built shelter. The entire castle is enclosed with a wall. Its length is 50 passa, its width is 20 and its circumference is 100 passa. The walls are approximately 140 passa, with four small towers in sets of two on each side and one tower in the middle of the entrance with a height of 10 passa. That means that it surpasses the walls about 5 passa. “We made the exterior shelter, which is made of stone blocks and has a length of 40 passa and a width of 15. The new walls of the castle were built approximately four months ago …”
It is immediately made clear that the dimensions that Zen describes correspond to the interior surrounding walls of the citadel of Panagia (length of 50 passa = 90 metres, width of 20 passa =36 metres and the total length of the castle’s walls 140 passa =252 metres).
It is also easy to identify the tower “in the middle of the entrance” with today’s central, cylindrical tower. The fact that today it stands a little lower than the 18 metres of Zen’s description is due to the fact that an original conical roof was subsequently destructed. On the contrary, the “four small towers in sets of two on each side” are no longer saved. Two of them can be placed with certainty at the two ends of today’s partition wall amongst the two surrounding walls, which at the time was the wall of the castle’s entrance. The N.W. end is strangely elevated and reinforced, while on its outside one can distinguish, even today, remains of a tower. The S.W. end has been demolished subsequently. It is at that point where the bastions are missing, while the exterior stonework presents intense traces of alteration (a recess forms). The position of the third tower must be sought in the polygonal rampart – of course with a different configuration – of its northern curtains interior enclosure. The position of the fourth small tower can be sought in the outpost area, of course it would have had a different form from its current one, at the East end of the interior enclosure of the citadel, which originally existed in the initial structure: The length of 90 metres that Zen describes coincides with the length of the interior surrounding walls, only if the outpost is also included.