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.
2,500 year celebration of the Persian Empire
The 2,500 year celebration of the Persian Empire (), officially known as The 2,500th year of Foundation of Imperial State of Iran (), consisted of an elaborate set of festivities that took place on 12–16 October 1971 to celebrate the anniversary of the founding of the Imperial State of Iran and the Achaemenid Empire by Cyrus the Great. The intent of the celebration was to demonstrate Iran's ancient civilization and history and to showcase its contemporary advances under His Imperial Majesty Mohammad Reza Shah, the last Shah of Iran.