The earliest remnant of the Aryan languages of Ariana which antiquity has bequeathed to us is the language of the Avesta, the sacred book of the Zoro­astrian religion.

For about nine hundred years the people of Ariana had no script in which they could write the Avesta. So they continued to learn it by heart and thus communicate it from generation to generation right from the seventh century B.C. to the third century A.D.

A special script was at last invented for this book in the third century A. D. The Avesta written in this particular script has been known as the Zend Avesta. At times it has been just mentioned as the Zend. The French scholar Anquetil du Perron who was the first to have studied it in India at the end of the twelfth/eighteenth century, introduced it to the West. For a considerable time it continued to be known as the Zend language in Europe. At present, however, the more accurate term of "Avestic language" is in vogue. The script in which the Avesta was recorded should be known as the "Zend script."

Much has been speculated on the origin and times of Zoroaster, and different theories have been advanced in this respect from the earliest times. What appears to be most authentic at present, however, is that Zoroaster preached his religion between 660 and 583 B. C. in the north-eastern zone of the Aryan plateau in Central Asia. It is plausible that he sprang from the Median stock, lived in the north-west of the present-day Ariana, and from there he travelled east to Central Asia. Of the extant languages and dialects of the Aryan plateau Pashto or Pakhto has the closest affinity with the Avestic language. This lends support to the view that the Avestic language was spoken in the north-eastern regions of the Aryan plateau in the seventh century B. C. The Avesta is a massive work, a major portion of which has been destroyed and forgotten owing to the vicissitudes of time and the domination of Ariana by foreign nations. What remains today of this book was compiled in the early days of the Christian era. It comprises fifteen out of the twenty-one original parts and if the extinct parts were proportionate in volume to those present about one-fourth of the book may be said to have perished.

From the philological point of view, the extant parts of the Avesta were not written in one period of history. On the contrary, its composition may be divided into three sections. The Gathas, which are composed in poetry, doubtlessly constitute the earliest part of the book. The Avesta is a collection.