Rhabdion
Mesopotamia, Turkey
Rhabdion (Ῥ, Rhábdion) was a Late Antique fortress of the Roman Empire, located on the Tur Abdin plateau to the northeast of Nisibis on the border with the Sasanian Empire. The fortress was later known as Qalʿat Haytham and is now identified with Hatem Tai, a fortification (kalesi, lit. 'castle') in south-eastern Turkey.
Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).