The history of the city is recorded on its walls and, at times, on the extant inscriptions, bearing witness to the repeated repairs and reconstructions of the walls over the course of the centuries. Remains from the Hellenistic and, subsequently, Roman fortifications of the city were incorporated in the late 4th century into the new fortification wall, trapezoid in shape, which encompassed Thessaloniki. The total perimeter of the city walls comes to 8km. On the plains, strong triangular redans alternated with square towers, while the wall was also strengthened with an outwork. On the sea side, the city was protected by a low fortification wall.
Part of the Early Christian wall and outwork is preserved at Dimokratias Square. This is where the main entrance to the city, the Golden Gate, stood until 1874, when it was demolished, serving as the starting point to the main road of the city, the Roman decumanus maximus and, subsequently, the Byzantine Leoforos. Part of the wall continues uphill along present-day Irinis Street, up to its junction with Aghiou Dimitriou Street, where the second main decumanus of the city was situated. This is where the second main gate of the city from the west, Litea, was located, leading to the provinces, the Mygdonian cirque and Liti.
The walls heading up towards the Acropolis follow the rocky geomorphology of the terrain. The NW section of the wall was added during the reign of Manuel II Palaeologus, who served as Despot of Thessaloniki from 1369 to 1373.
Acropolis Walls – Laparda Tower – Anna Palaeologina Gate – Trigonion Tower or Alysseos Tower.
The so-called intermediate wall (diameso) that separated the Acropolis from Ano Poli (the Upper City) extended to the west, approximately opposite Vlatadon Monastery, and reached Trigonion Tower to the east. The erection of towers on the intermediate wall towards the interior of the Acropolis, which originally formed the external facade of the city wall, confirms the subsequent addition of the Acropolis to the initial fortification walls. The extant inscriptions on the rectangular tower known as Laparda Tower, which stands opposite Vlatadon Monastery, concern the extensive interventions on the fortification of the Acropolis in the 12th century.
Following the intermediate wall towards the NE stands the Gate of Anna Paleologina (1355-1356), as noted on the inscription carved into the marble doorframe. This gate led to the area outside the walls.
The intermediate wall ends in the NE at Alysseos Tower or, as it is better known, Trigonion Tower. This is a circular tower constructed in the 15th century, incorporating an older square tower that stood at that location, forming part of the Byzantine fortifications.
Trigonion Tower, along with the Vardaris Fort and the White Tower, were incorporated in the new fortification strengthening system applied by the Ottomans in their effort to adapt to changes in military tactics brought about by the use of gunpowder.
Eastern Walls – White Tower – Outwork
The walls, at times built on rocky hills and at times on the remains of Roman fortifications, head downwards, proud and stately, to Aghiou Dimitriou Street and from there, almost humble, after 1889, to the sea. Through Filikis Etairias Street, where visible sections of the outwork and triangular redans of the main wall are preserved, they reach the White Tower, which stands at the junction of the sea wall and the land wall. The tower, in its present-day form, was built in the 15th century as a part of the modernisation of fortifications, replacing an older Byzantine tower.
From the gates of the eastern section of the wall, the locations of two main gates are known, situated on the two main road axes of the city: the New Golden Gate, corresponding to the Litea Gate, and the Cassandreotiki Gate (or Kalamaria Gate), corresponding to the Golden Gate.
The Heptapyrgion fort stands at the highest point of the Acropolis, on the NE end of the city walls. It is a complex of various construction phases from the Early Christian – early Byzantine period up to the years of Ottoman rule, with the addition of newer buildings and auxiliary areas when it was converted into a prison in the 19th century, and, finally, during the late 1990s, mild interventions and necessary conversion took place so that the building could house the offices of the 9th Ephorate of Byzantine Antiquities.
On the walls of the fort complex, with its numerous ceramoplastic and marble architectural elements from various eras incorporated at various points, numerous phases of construction can be detected, equal and corresponding in number, and the many adventures of the building over time, interwoven with the long and tumultuous history of the city, are depicted.
The original core of the fort consists of ten towers, eight four-sided ones and two triangular ones, along with their intermediate sections, the oldest being the northern section, which was incorporated in the layout of the Early Christian fortification of the Acropolis, with numerous subsequent interventions. During the Middle Byzantine era, the towers on the southern side were added, completing the enclosure of the fort. The marble Ottoman inscription of 1431, built into the wall above the transom of the main entrance, denotes interventions and renovations to towers and sections of the fort during the years after the conquest of the city and its last refuge, the Heptapyrgion.
Written sources on the fort are either silent, as is the case in the early Byzantine era, or sparing and confused, as is the case in the Middle and Late Byzantine eras, where references to the Koulas of Thessaloniki are at times related to the Heptapyrgion and at times to the Acropolis. The name Heptapyrgion occurs during the Ottoman era, possibly imitating Yedi Kule (Seven Towers), a 15th century fort in Istanbul with an equal number of towers.
The monument indeed, burdened with its very recent memory of being a prison, which its new use not only failed to eradicate but actually preserved and showcased in the exhibition operating on the ground floor of one of the newer buildings of the complex, is open to the public of the city every day, while its premises, both open and closed, are made available for cultural events under the auspices of the 9th Ephorate of Byzantine Antiquities.