Certain towns in Oman perhaps were dominated politically and militarily by Parthian and later Sasanian invaders from Iran.
In late 588, a massive army of Turks invaded the eastern provinces of the Sasanian empire, reaching as far as Badghis and Herat.
It is known to have been occupied, at least, during the Akkadian, Old Babyonian, Kassite, Sasanian and Early Islamic periods.
By the time of the Parthian and the Sasanian dynasties, iwan had emerged as two types of structure: the old columned one, and a newer vaulted structure—both, however, carrying the same native name of apadana/iwan, because both types are "unprotected" (open on one side to the elements).
The dynasty was founded by the founder of the Bvads, Baw Ka'usiyeh, the first prince of Tabaristan (r. 665–680) son of Kawus, son of Kavadh I, the Sasanian Emperor.
Firuzabad is a settlement built under Adaschir I and a well-documented example of Sasanian urban planning.
In 242, the Roman emperor Gordian III set out against the Sasanians with “a huge army and great quantity of gold,” (according to a Sasanian rock relief) and wintered in Antioch, while Shapur was busy in subduing Khwarezm and Gilan.
The Gashnaspians ruled the region until 528 CE, when, after a long period of fighting, the Sasanian King Kavadh I defeated the last Gashnaspian king.
After the Sasanian disaster, Yazdegerd fled to Isfahan and then Estakhr where he tried to organize a base for resistance in the province of Pars.