The most ancient copies of the Zend-Avesta are only to be found in Pehlivi characters, a Persian alphabetic system of the Sassanian period, dating from the 3d century A. D.
The Pehlivi alphabets are direct descendants of the Aramean alphabet, a daughter of the older Phœnician, which had developed in the highlands of Aram, or Upper Mesopotamia, before the Achamenian period in Persia.
The Aramean language originally expressed by these characters, was at this time one of the most widely spoken of the Semitic dialects, including the idioms of Syria, Aram and Assyria.
At first, as a commercial and literary script, it came to be extensively used in these and adjacent countries conjointly with the cuneiform.
In the ruins of ancient Nineveh, there are the remains of what must have been a public registry office. From this a great number of terra cotta tablets have been exhumed on which were inscribed in cuneiform characters records of legal contracts, including loans of money, sales of estates and exchanges of other properties. Many of these tablets were docketed on the sides or edges in Aramean or Phœnician letters, by which the subject of each document could be readily found when piled on the shelves or in recesses where they were deposited. Reference in some of these appears from the time of Tiglath Pileser and Sennacherib, 741 to 681 B. C.
Other evidences of the extensive use of this script comes from the later Assyrian kings, and from Babylonia, until the decline of these empires, 606 to 538 B. C.
After the conquests of Babylonia by the Persians, the Aramean alphabet gradually became the official script of these regions, finally supplanting the cuneiform.
Of historic documents of this period in the Aramean script and language was the royal decree given by Artaxerxes to Ezra for the rebuilding of the temple at Jerusalem.
The Aramean was the language spoken at this time by all the Semitic people of Babylonia.
It is probable that during the whole period of the Achæmenids a local variety of the Aramean alphabet was in general use as a cursive script throughout the empire.