According to an account on the fall of the city by the historian Ioannis Anagnostis, the large round north-eastern tower of the Thessaloniki fort was named Trigonion Tower by researchers and was built at the same time as the White Tower following Thessaloniki’s occupation by the Ottomans, probably in the second half of the 15th century. The tower has a cylindrical structure with a height of 20-22m and a diameter that decreases as the height increases [from 24.85 m at its base to 23.45m at the level of the cupola]. The gradient of the outer surface, which is formed by the reduction in its diameter, is more striking up until the level of the curved stone cornice surrounding it, to which it owes its Ottoman name “Zincirli or Kusakli Kule”, which translates as “Chain Tower”. The Tower was built in order to deal with the new war technique of using firearms and its entire design serves this purpose, such as the considerable thickness of its masonry and its round shape, which were dictated by the need to ricochet the bullets fired at it and to ensure surveillance of the surrounding areas. The design also includes two protruding structures on the south and west sides, which served as an observatory and machicolation, respectively.

Access to the Tower is from the west via a wooden platform that is supported by a contemporary metal structure. The entrance is succeeded by a square space that is covered by a low dome leading to two staircases. The one staircase has a north-westerly direction while the other an easterly direction, and both lead to the first storey, particularly to three vaulted spaces that served as artillery chambers and to an observatory–latrina, which are arranged in a circular fashion and are placed on the outside of the Tower. The north-western staircase further leads to the second storey, and on the left side of the staircase stands a guard post for guarding entry to the area, which is built into the northern Byzantine wall. On the right lies a closed rectangular space that served as a powder deposit (currently housing a screening room and information boards) and another space used by the garrison to guard the entry into the Tower. This is the space where the main elements of fortification architecture can be detected, such as the position of the portcullis mechanisms, the through-holes that functioned as murder holes, as well as the infrastructure supporting them (the fireplace and water tank).

The presence of a pre-existing large rectangular tower of the early-Byzantine fortification was discovered through excavation within the Tower, thus necessitating the restructuring of the initial design of the second storey. The top of the monument is supported by crenellations designed to defend the Tower.

During the years 2007-2008, in the frame of the Operational Programme 'Culture' of the 3rd EU CSF there have been conducted restoration and infrastructure works so as to make the monument accessible to visitors.

Trigonion Tower
Trigonion Tower
Trigonion Tower
Trigonion Tower