During the first half of the 1st millennium CE, an empire arose in Persia that extended its power and influence to Mesopotamia in the east, Arabia in the south, the Caucasus Mountains in the north, and as far east as India. This empire, known alternatively as the Sasanian Empire or Sassanid Empire, was the last of three great dynasties in Persia - the Achaemenid and the Parthian being the first two dynasties - before the rise of Islam. In fact, many scholars consider the Sasanian Empire to be the last great empire of the ancient Near East because once it had been obliterated, Islam became the standard religion of the region, ushering in the Middle Ages.

Thanks to the Sasanians' efforts with regard to religion, modern scholars know much more about Zoroastrianism than they would have if the religion continued to disseminate orally. Their efforts also protected Zoroastrian knowledge in later years after the dynasty was long gone and Islam became ascendant in Persia.

The Sasanians, like the Achaemenids and Parthians, also carried forth the Persian conflicts with the Hellenic world. Although the Achaemenids fought the Macedonian Greeks and the Parthians challenged the imperial Romans for control of Mesopotamia, the Sasanians faced Rome in its later stages of collapse and subsequently fought the revitalized Byzantine Empire. An examination of Sasanian chronology and culture reveals that it was a much more important dynasty and empire than most may think.

The Sasanians also had a profound global influence through one of the most idiosyncratic religions of the ancient Middle Eastern world: Manichaeism. Like Zoroastrianism, the Manichaean religion has a rich history, as seen in its interactions with early Christianity and its unparalleled emphasis on secrecy. These exceptionally mysterious elements have appealed to the curiosities of thousands of scholars who have studied the development of this ancient belief system and where it came from. Manichaeans primarily revere the teachings and life of their prophet Mani who formed a synthesis of various religious traditions contemporaneous to his life. Although hardly a well-known religion in modern days (and, quite likely, an extinct religion in terms of practitioners), the Manichaean religion is an important witness to the development and interchanging ideas seen in early Iranian and Christian religion.

Many scholars have been fascinated with the beliefs and teachings of Manichaeism, dating as far back as the early Church. Christian theologians who acted as heresy hunters (including Augustine of Hippo) took it upon themselves to attack Mani's new religion on the grounds that it was just another dangerous heresy that had cropped up in the fertile ideological soils where the powerful Roman and Persian worlds collided. As such, Manichaeism was dismissed as an aberration of the truth and was critiqued in many writings of orthodox church leaders. This remained a powerful influence for scholars all the way up to the 20th century, largely due to the fact that few if any original Manichaean writings had survived the centuries.

Modern studies of Manichaeism began in the 1930s at the hands of Hans Jacob Polosky and Carl Schmidt, who announced the discovery of new 4th century Manichaean codices which detailed the beliefs of Manichaeism in greater depth than any prior text. Reliance on the polemics of heresiologists from both the ancient and medieval periods came to an end and the Manichaean faith could be studied on its own terms. Previous concepts about what Manichaean faith was had to be dismantled to make way for what these ancient believers in this mysterious religion actually had to say for themselves.