Old Persian was an ancient type of persian(Farsi) which the Achaemenid dynasty used to speak. The first written findings in this language is the Behistun inscription, dating back to 6th century BC. Old Persian(Farsi) used cuneiforms in its writing system, which does not seem to be used by the public during the Achaemenid reign, except for literary purposes and for carving the inscriptions. At the same time, other accents of old Persian(Farsi) were extant and had gradually evolved in parallel with the other four significant languages of ancient era: the Bactrian language, the Sogdian language, the Parthian language, and the Khwarezmid language.
Old Persian covers from 20th to approximately 3rd century B.C. Four dialects of Old Iranian languages are: the Median language, the Saka language, the Avestan language, and Old Persian. The Median language was prevalent in Western Iran and among the Medes, while the Saka language was spoken in North, covering an area from the borders of China to the Black Sea, and by Parthian tribes and Sogdia residents. Only few words and phrases from various writings still remained from the aforementioned two languages. However, there is abundant evidence related to Avestan and Old Persian languages. For instance, Zoroaster has written his book in the Avestan language.