Oltu Castle, locally known as Oltu Kalesi, lies in the town with the same name, in the province of Erzurum in Turkey.
The first fortification, on this steep rock next to the Oltu River, was probably built in Urartian times, during the Iron Age. Later, the castle was built and restored by subsequent rulers; amongst them the Byzantines, the Seljuqs during the 11th century and, from the mid-16th century on, the Ottomans. During the Ottoman period Oltu Castle was also used as a caravanserai. At some point in time, one of the northern bastions of the castle was used as a tomb.
Oltu Castle was built out of ashlar masonry. The castle we see today is only the inner bailey. The much larger outer bailey, which encompassed the old town of Oltu with thick walls and towers, was completely destroyed.
This is all the information I was able to find about Oltu Castle. So, if you know more, please mail me.
Oltu Castle can be visited but only on Fridays. This I learned only after I had returned home, so it was closed when I visited. Too bad, it looks like a great castle.