If Topkapı Palace represents the most sophisticated side of the Ottoman power, the Yedikule Fortress stands for its darkest face. As La Bastille in Paris and Alcatraz in San Francisco, Yedikule Hisarı (“Fortress of Seven Towers”), is the most dreadful dungeon in the history of Istanbul.
Also known as Yedikule Zindanları, it was built after the conquest of Constantinople by Mehmet II by adding three new towers to the existing Byzantine walls, at the level of the famous Golden Gate. In the Ottoman period it was used as a treasury and archive but, as already mentioned above, it's best known for being used as a prison. In Yedikule they were imprisoned, among others, Romanian rulers Prince Petru Cercel, Constantin Brancoveanu with his children, Sultan Osman II, David Komnenos, last emperor of Trebizond, and Simon I, King of Georgia. Yedikule Fortress has been a museum since 1895, later on we will go into details about visiting possibilities.
In order to understand the origins of this citadel we have to go back to roman times, more precisely to AD 390, when Theodosius I erected a triumphal arch which at that time stood by itself because the city walls had not been built yet. The name of this arch was Porta Aurea (Golden Gate), which travelers described as “glittering with gold”. When Theodosius II decided to extend the city walls two decades later he incorporated the Golden Gate within his new land walls. On many occasions this Golden Gate became the scene of triumphal entries by Byzantine emperors: Heraclius (629) after defeating the Persians; Constantine V, Basil I and Basil II (VIIIth century) after the victories over the Bulgars; and Theophilus and his son Michael III (IXth century) after their victories over the Arabs. The last triumphal entrance was the one of Michael VIII Palaeologus (1261), who recaptured the city from the Latins after the Fourth Crusade. Then in a context of continuous defeat, the Golden Gate was walled up for defense, never again to open.
In 1457, four years after the conquest, Mehmet II started a program of architectural reconstruction, replacing the former Byzantine legacy as an attempt of legitimation. For instance, Topkapı Palace was built on the exact place of the Byzantine acropolis and Hagia Sophia was transformed into a mosque. In the same line, Yedikule Fortress was built on the premises of the Golden Gate in the Theodosian Walls.
The darkest side of the history of Yedikule Fortress is related to its use as dungeon for the internal and external political enemies of the Sultanate. Among many others we can stand out the execution of David of Trebizond (1463), the last member of the Komnenos family and last emperor of Trebizond; the execution of Simon I the Great (1611), King of Georgia; the assassination of Sultan Osman II (1622), who dared to face the Janissaries with fatal consequences; and the Romanian prince Constantin Brancoveanu (1714), who was beheaded with his four sons and who has a memorial plaque since October 2013. Not less interesting are the inscriptions that can be seen on the walls made by the desperate foreign ambassadors in their hopeless days of confinement. 
Despite its outstanding interest as one of the few monuments that combines the roman, Byzantine and Ottoman heritage, it remains a secret jewel for the public eye. For the eager tourist who wants to unveil the mysteries of Yedikule, the fortress is open in summer season (right now is closed due to management reasons) for the price of 10 Turkish lira. Visitors can directly reach it from taksim by bus 80T, from Eminönü by bus 80 and with Marmaray metro line (Kazlıçesme stop).
As a closure, let us share a legend that still dwells among the ruins. According to it during the last combats of the siege, when the Ottomans were breaking into the city, an angel rescued Constantine XI, turned him into a marble statue and hid it beneath the Golden Gate. Who knows, maybe during your visit the last Byzantine emperor wakes up to finally retake the city and restore its former glory.[box type=”info”] Special thanks to Dragoş Diac for helping me write this article![/box]