Bursa was formed by the Bithynians in the 2nd century BC who came and settled to the area in the 7th century BC and later on became an independent kingdom in 327BC. With the suggestion of General Hannibal who escaped the Romans and took refuge in Bithynia, the Bithynia King Prusias built a city he named Prusias ad Olympum in 185BC on top of a hill and surrounded it with walls. Over time, the city’s name Prusias became Prusa and later on Bursa. Built by the Bithynians, the Bursa Castle suffered damages during various sieges over time and has undergone several repairs during the Roman, Byzantine and the Ottoman Empire eras. During the Orhan Gazi era who added Bursa to the lands of Ottoman Empire in 1326, the walls were supported by bastions (towers). Famous Ottoman Traveler, Evliya Celebi who visited Bursa in 1640 stated that the castle had 67 towers, 5 gates and that the surrounding area is 10,000 steps. The walls are approximately 2 kilometers long and the gates are named Hisar (Saltanat), Kaplica, Zindan, Pinarpasi (Su), Yer (Zemin) gates.