Yoros Castle Yoros Castle ( ) is a ruined castle at the confluence of the Bosphorus and the Black Sea , to the north of Joshua ' s Hill , in Istanbul , Turkey . It is also commonly referred to as the Genoese Castle , due to Genoa ’ s possession of it in the mid - 15th century . Geography . Yoros Castle sits on a hill surrounded by steep bluffs overlooking the Bosphorus . It is just north of a small fishing village called Anadolu Kavağı , on Macar Bay , and the entire area is referred to as Anadolu Kavağı . This section is one of the narrowest stretches of the Bosphorus , and on the opposite shore sits an area called Rumeli Kavağı , which formerly held a fortification similar to Yoros Castle . ( Anadolu and Rumeli were Ottoman terms for the Anatolian and European parts of the empire ) . History . Strategically set near the confluence of the Bosphorus and the Black Sea , the future site of Yoros Castle was settled by the Phoenicians and Greeks prior to the Byzantine period for trading and military purposes . The Greeks called the area Hieron ( Sacred Place ) . The remains of temples , including Dios , Altar of the Twelve Gods , and " Zeus Ourios " ( Zeus , granter of fair winds ) were discovered in the area , dating to centuries BCE . Yoros Castle was intermittently occupied throughout the course of the Byzantine Empire . Under the Palaiologos dynasty during the decline of the empire , Yoros Castle was well fortified , as was the Rumeli Kavağı on the opposite side of the Bosphorus . A massive chain could be extended across the Bosphorus between these two points , cutting off the straits to attacking warships , similar to the chain across the Golden Horn which was used to defend Constantinople during the last Ottoman siege by Sultan Mehmed II . Byzantines , Genoese , and Ottomans fought over this strategic fortification for years . It was first conquered by Ottoman forces in 1305 , but retaken by the Byzantines shortly thereafter . Bayezid I took the castle again in 1391 while preparing for his siege of Constantinople . It was used as his field headquarters during the construction of Anadoluhisarı , one of the more important castles for the siege . In 1399 the Byzantines attempted to take back Yoros Castle . The attack failed , but the village of Anadolu Kavağı was burned to the ground . The Ottomans held the fortress from 1391 – 1414 , losing it to the Genoese in 1414 . The forty - year Genoese occupation lent the castle its moniker of Genoese Castle . Upon Fatih Sultan Mehmed ’ s conquest of Constantinople in 1453 , the presence of the Genoese at such a strategic location posed a threat to the new Ottoman capital . Within a few years , Sultan Mehmed drove the Genoese out . He then fortified the walls , and constructed a customs office , quarantine , and check point , as well as placing a garrison of troops there . Bayezid II ( 1481 – 1512 ) later added a mosque within the castle walls . Cossack raids had plagued the Ottoman Empire throughout its long history . In 1624 a fleet of 150 Cossack caiques sailed across the Black Sea to attack towns and villages near Istanbul . They struck villages inside the Bosphorus , and Murad IV ( 1623 – 1640 ) refortified Anadolu Kavağı to defend against the fleet . It would prove instrumental in securing the region from seaborne Cossack raids . Under Osman III ( 1754 – 1757 ) , Yoros Castle was once again refortified . Later , in 1783 Abdülhamid I added more watchtowers . After this period , it gradually fell into disrepair . By the time of the Turkish Republic , the castle was no longer used . Present Day Yoros Castle . The ruins of the citadel and surrounding walls still exist , though the mosque , most of the towers , and other structures are gone . Yoros Castle and the village of Anadolu Kavağı are a popular day trip from Istanbul . Typically , the site is not supervised and visitors are free to climb all over the ancient walls . However , there are currently archaeological excavations going on and visitors are unable to enter the castle . Greek inscriptions remain etched on the walls of the castle to this day , along with the symbol of the Palealogus family , who ruled Byzantium until its fall . The military importance of the site cannot be overstated . In fact , much of the area surrounding Yoros Castle is today in the hands of the Turkish military , who have closed off areas to visitors . Anadolu Kavağı . The villagers of Anadolu Kavağı historically depended mostly on fishing for income , but it appears some may have acted as ' wreckers ' . Turkish rumors report that they would light fires in order to disorient ships and ground them in the narrow straits , seizing their goods . Conversely , many claim that Anadolu Kavağı was also used as a shelter for trade ships against storms , where it is recorded even up to three hundred ships were serviced at a time .