Arbāyistān (Old Persian: Arabāya-stāna) is mentioned in Shapur I's inscription on Ka'ba-ye Zartosht.[2] According to historian Widengren, the name was lent from the Arabs inhabitant of Upper Mesopotamia.[2] The term Arbāyastān literally means "The Land of Arabia/Arab", where Arbāy or Arabāya is ("Arabia") and the suffix -istān ("Land of").[3] Although the name Arbāyistān appears to be used when referring to northern Mesopotamia, Osroene was not included.