List of ancient great powers
The Sassanid Empire is the name used for the fourth Iranian dynasty, and the second Persian Empire (226–651). The empire's territory encompassed all of today's Iran, Iraq, Armenia, Afghanistan, eastern parts of Turkey, and parts of Syria, Pakistan, and large parts of Caucasia, Central Asia and Arabia. During Khosrow II's rule in 590–628 Egypt, Jordan, Palestine, Lebanon were also briefly annexed to the Empire, as well as far west as western Asia Minor. The Sassanid era, encompassing the length of the Late Antiquity period, is considered to be one of the most important and influential historical periods in Iran. In many ways the Sassanid period witnessed the highest achievement of Persian civilization. The empire is furthermore known for being the arch-rival of the neighboring Roman–Byzantine Empire for a period of over 400 years. As the Parthians were replaced by the Sassanids, they carried on the already century long lasting Roman–Persian Wars, which would eventually become the longest conflict in human history.
Greater Iran
While up until the end of the Parthian period in the 3rd century CE, the idea of "Irān" had an ethnic, linguistic, and religious value, it did not yet have a political import. The idea of an "Iranian" empire or kingdom in a political sense is a purely Sasanian one. It was the result of a convergence of interests between the new dynasty and the Zoroastrian clergy, as we can deduce from the available evidence. This convergence gave rise to the idea of an Ērān-šahr "Kingdom of the Iranians", which was "ēr" (Middle Persian equivalent of Old Persian "ariya" and Avestan "airya").