 He spent many years at war against the Hephthalites.According to the "Šahrestānīhā ī Ērānšahr" ("The Provincial Capitals of Iran"), Yazdegerd II fortified the city of Damghan and turned it into a strong border post against the Hephthalites.It was sometime during this period that Yazdegerd II created the province of "Eran-Khwarrah-Yazdegerd" ("Iran, glory of Yazdegerd"), which was in the northern part of the Gurgan province.