Persians are an ethnic group defined primarily by language and location. The Persian language, also known as Farsi, which linguists classify in the Indo-Iranian Branch of the Indo-European Language Family, had about 23 million speakers in Iran in 1986 and 6 million in Afghanistan the same year (Grimes 1988). It is the official language of Iran, and also the language of Iran's government bureaucracy, educational institutions, mass media, and literature. A dialect of modern Persian is used as the language of elites in Afghanistan. Standard Persian, or Farsi, followed Middle Persian, or Pahlavi, which was the language of the Sāssānian period of Iranian history ( A . D . 224 to 642). In the centuries that followed the Arab conquest of Iran, Pahlavi absorbed numerous Arabic elements. The addition of Arabic words into Persian is the primary difference between the language spoken today and that spoken thirteen centuries ago.