When the Turks arrived in Üsküdar under the rule of Orhan Gazi, the Ottomans became a major player on the forefront. Along with the Ottomans there had been three other strong powers that had deep desires of controlling the Bosphorus, they included, the Venetians, Genoeses and the Byzantines. Naturally, a political dogfight started between the powers. It was a time for change, new alliances were formed however, the two Italian powers, Venice and Genoa, would never stay on the same side due to their pursuit for power. They had strong economic influences in the region as well as a very well organized trade route and their only motivation was trade. Genoa especially, had a great trade route on the Black Sea and the relations between Genoa and the Ottomans were generally good. Meanwhile, relations between the Byzantines and Ottomans weren't that great. They had periods of peace and periods of violence, but most of the time they were doubtful of each other. Nerves were stretched to a point that was enough to demolish constantinople's walls.
The tension started on the Bosphorus shores at the beginning of the 1390s. The Byzantine Emperor, Yoannis Paleologos, ordered a construction aiming to fix the city walls of constantinople. This action by the Byzantine Emperor made the Ottoman sultan, who was busy in Anatolia, very angry and led him to insult the Byzantine Emperor. Sultan Bayezid then requested a demolition of the overhauled part of the city walls. Emperor Yoannis Paleologos was in desperation because his son Manuil Paleologos, the only faction heir, was in Bursa to join Sultan Bayezid's Anatolian assault. Having no other choice, the repaired parts of the city walls were demolished. However, the Byzantine emperor was a proud man, he couldn't bring himself to become a vassal, and eventually died of a nervous breakdown. This was due to his continued humiliation by the Ottoman sultan.
The moment that Manuil Paleologos heard the news of his father's death, he escaped from the Ottoman palace in Bursa and arrived in Constantinople to ascend the throne and finally begin to rule the Byzantine Empire. Not so much time had passed since he became emperor that Sultan Bayezid had sent a messenger to ask that a Turkish town be built in Constantinople, along with a mosque and a “kadı” to be at the head of this town. The sultan's requests were immediately declined. Consequently, Sultan Bayezid began to establish his permanent rule over a series of villages on the European coast thanks to an alliance with Genoa. Therefore, Emperor Manuil Paleologos was locked inside the city walls and his rule was recognized only in Constantinople. Still, Ottoman sultan had a great interest in taking Constantinople from him. Sultan was aware of his lack of cannons so he was not able to demolish the city walls. However hunger was a tool he could use to help him reach his goal. By keeping the Emperor locked inside the city walls with no access to the outside world, he would eventually run out of food forcing him to take action. Thus, Sultan Bayezid became the first Ottoman sultan who besieged Constantinople. His war against Constantinople continued between 1390 and 1402 and during this period the Ottomans besieged Constantinople four times.
Around this time Venice and Genoa remained silent and as a result the Byzantines had no real power to fight against the Ottomans. In preparations for his sieges of Constantinople, Sultan Bayezid, ordered the construction of the Anadolu Hisarı, known as the Anatolian Fortress in English. He had already known the best location for his castle was the site of the ancient Jupiter temple on the narrowest point of the Bosphorus (660 meter). The construction began on the Asian shore, where the beautiful Göksu River pours into the Bosphorus, and was completed almost in a year between 1394 and 1395.
Anadolu Hisarı was composed of an inner square castle surrounded by walls on all sides and strengthened by a few towers. The main castle was a quadrangle design and its wall thickness changed between 2 and 3 meters. The three towers were all designed differently with different shapes such as a horseshoe, half round and cylindrical. During that time artillery had not yet been devolved in Europe so it was designed to cope with catapults and similar siege engines. Thus, Sultan Bayezid was able to control the Bosphorus, which would eventually help him enter Constantinople.
In 1396 an anti-Ottoman crusade led by the Hungarian King, Sigismund of Luxemburg, failed fighting in the Battle of Niccopolis on the 25th of September, and on his return decided to punish his rival Emperor Manuil Paleologois who had promoted a war against Ottomans in Europe. His fortress in Beykoz was already built when he returned back. Manuil Paleologois received a message from the sultan once again. They brought the same requests to the Byzantine emperor, which once again included, a Turkish town in Constantinople, a mosque, and a “kadı” at the head of the town. Manuil Paleologos declined the sultan's requests yet again. This resulted with another siege of Constantinople by Sultan Bayezid. The Byzantine emperor had no other option, he knew that Constantinople could not stand by itself and therefore accepted the sultan's rule. Thus, the first Turkish town in Constantinople was finally established.
In 1402 Sultan Bayezid lifted the siege and turned his focus on to Timur, who came from afar, but with an enormous army. The two big Muslim power's meeting was known as the Battle of Ankara. It resulted in a major victory for Timur, who took the Ottoman Sultan Bayezid away in chains on the battlefield. This event led to a period of crisis for Ottoman Empire but on the other hand gave Emperor Manuil Paleologos some space to breathe.
In the spring of 1452, across the waters from the Anatolian Fortress, Sultan Mehmed II built the Rumelian Fortress in order to guarantee the control of Bosphorus. During the construction some changes were made in the Anatolian Fortress as well. After the conquest of Constantinople in 1453 this small fortress lost its importance and became a prison for the guilty janissary soldiers. Which in turn became a residential, small village. Parallel to the growth of the civilian population, construction also grew. A mosque and a Turkish bath were built. The number of houses built depends on what information is found. According to Evliya Çelebi there were 1800 houses in the village during the 17th century but according to the document from the first Ottoman constitution of 1876, there were only 167 houses in the village. It's a huge gap in between the two but the actual number is not certain. In historical documents both the village and the castle were called “Güzelce Hisar” which means, “pretty castle”.
After the foundation of the Turkish Republic, the Istanbul municipality restored the Anatolian Fortress. Shortly after, the roadway was built between Beykoz and Üsküdar and it passed directly in the middle of the fortress, which led it to lose its original appearance. While the roadway was being constructed, the wooden houses that stood nearby the Anatolian Fortress were first publicized and then demolished to make the fortress look nicer.
The Anatolian Fortress is the oldest Turkish architectural structure built in Istanbul. It's smaller in size when you compare it with the Rumelian Fortress on the opposite side of Istanbul. It is now an open-air museum but only the outer walls can be seen. So, the best you can do is buy some “börek” or “simit” and a Turkish tea, sit on the nearby bench in the park next to castle, and enjoy your time. The only problem is the noise may drive you crazy because a road passes just through it.
Still, the importance of Anatolian Fortress was and still is crucial for the history of Ottoman Empire.