The castle, built 2300 years ago by Bithynians, housed Bithynia Palace and Ottoman Bey Palace in old times. The Bursa Castle was built on the area involving Pinarbasi, Alacahirka, Ortapazar, Kavakli and Tophane.
Today, very few of the walls of the castle are still standing. They were heavily damaged during the attacks of the Romans and Ottomans. The huge Sultanate Gate on Tophane Street was restored in 2005. The length of the walls reach 2 kilometers.