What language was used for official documents in the Sassanid Empire?

Middle Persian was used for official documents in the Sassanid Empire. Also called Pahlavi in many contexts, it was the southwestern Iranian language associated with the Sasanian ruling house and became the empire’s principal administrative and literary language.

The language descended from Old Persian, the language of the Achaemenid Empire, and was written mainly in scripts derived from Aramaic. Royal inscriptions, religious works, administrative texts, and Zoroastrian literature preserve Middle Persian from the Sasanian period and the centuries immediately after it.

The empire was multilingual, so Middle Persian was not the only language in use. Parthian remained important among eastern Iranian populations and aristocratic families, while Aramaic continued to be widely spoken and written, especially in Mesopotamia. Greek also appeared in some early Sasanian inscriptions. Even so, Middle Persian increasingly replaced Parthian and Aramaic for central administration and official state inscriptions.

Middle Persian later developed into Early New Persian, the ancestor of modern Persian. Its religious form, often called Zoroastrian Pahlavi, remained in use among Zoroastrian communities after the fall of the Sasanian Empire.