Kayseri Castle The impressive walls of Kayseri Castle were originally constructed by Roman Emperor Gordian III in the 3rd century, and later reconstructed by Byzantine Emperor Justinian. However, it was mostly built in the 13th century by Seljuk Sultan Alaattin Keykubat I, after being repaired twice due to collapses by Karamanoğulları and Osmanoğulları. Located in the center of Kayseri and protecting the transportation routes in Central Anatolia, the castle was built on a flat surface and consists of two parts - the Outer Castle and Inner Castle. The Inner Fortress is situated higher than the Outer Fortress and is surrounded by fortification walls, making it a separate fortress. There are 18 towers in total. The Outer Castle, which includes administrative centers, housing areas, and fortification installations, serves to protect the city with its walls and bastions, and surrounds the ancient state halls. During the Turkish period, the surrounding walls and bastions of the Inner Castle were upgraded, and changes were made to its use. Since there was no longer a need to defend the city during the Ottoman period, neighborhoods were established within the Inner Castle, and the Fatih Mosque was built during this time.