The Persian Empire (Persian: شاهنشاهی ایران, translit. Šâhanšâhiye Irân, lit. 'Imperial Iran') refers to any of a series of imperial dynasties that were centred in Persia/Iran from the 6th century BC Achaemenid Empire era to the 20th century AD in the Qajar dynasty era.
The first dynasty of the Persian Empire was created by Achaemenids, established by Cyrus the Great in 550 BC with the conquest of Median, Lydian and Babylonian empires. It covered much of the Ancient world when it was conquered by Alexander the Great. Persepolis is the most famous historical site related to Persian Empire in the Achaemenid era and it has been a UNESCO World Heritage Site since 1979.
The Persian Empire in the Sasanian era was interrupted by the Arab conquest of Persia in 651 AD, establishing the even larger Islamic caliphate, and later by the Mongol invasion. The main religion of ancient Persia was the native Zoroastrianism, but after the seventh century, it was slowly replaced by Islam which achieved a majority in the 10th century.
The Safavid Empire was the first Persian Empire established after the Arab conquest of Persia by Shah Ismail I. From their base in Ardabil, the Safavid Persians established control over parts of Greater Persia/Iran and reasserted the Persian identity of the region, becoming the first native Persian dynasty since the Sasanian Empire to establish a unified Persian state.
Literature, art and architecture flourished in the Safavid era once again, and it is often cited as the "rebirth of the Persian Empire". Safavids also announced Shia Islam as the official religion in the empire versus the Sunni Islam in the neighbouring Ottoman Empire.