Classical Persian, the literary form of New Persian, emerged in the ninth century in the eastern Iranian lands, where local courts revived Persian as a written language after two centuries of Arabic dominance following the Islamic conquest. Written now in the Perso-Arabic script and absorbing a large Arabic vocabulary, it stood in direct descent from the Middle Persian of the Sasanians and, behind that, the Old Persian of the Achaemenids.
Ferdowsi's Shahnameh, completed around 1010, fixed the language's prestige with sixty thousand couplets of epic, and a canon followed that ranks with any in world literature, Omar Khayyam, Nizami, Saadi, Rumi, Hafez, Jami. Persian became the great court and cultural language of the eastern Islamic world, used far beyond Iran by Turkic, Mongol and Indian dynasties.
Ottoman gentlemen read Hafez, and in South Asia Persian served as the administrative and literary language of the Delhi Sultanate and the Mughal empire for centuries, so that a single classical register connected Sarajevo to Bengal. The modern standard languages of Iran, Afghanistan and Tajikistan descend from it directly, and educated speakers still read the classical poets without translation, a continuity of a thousand years.