Instead of a combination of as many as ten and fifteen wedges to make one sign, we have in the Persian never more than five, and frequently only three; and instead of writing words by syllables, sounds alone were employed, and the syllabary of several hundred signs reduced to forty-two, while the ideographic style was practically abolished.
The second style of cuneiform, generally known as Median or Susian,[13] is again only a slight modification of the "Persian." Besides these three, there is a fourth language (spoken in the northwestern district of Mesopotamia between the Euphrates and the Orontes), known as "Mitanni," the exact status of which has not been clearly ascertained, but which has been adapted to cuneiform characters.

A fifth variety, found on tablets from Cappadocia, represents again a modification of the ordinary writing met with in Babylonia.

In the inscriptions of Mitanni, the writing is a mixture of ideographs and syllables, just as in Mesopotamia, while the so-called "Cappadocian" tablets are written in a corrupt Babylonian, corresponding in degree to the "corrupt" forms that the signs take on.

In Mesopotamia itself, quite a number of styles exist, some due to local influences, others the result of changes that took place in the course of time.

In the oldest period known, that is from 4000 to 3000 B.C., the writing is linear rather than wedge-shaped.
The linear writing is the modification that the original pictures underwent in being adapted for engraving on stone; the wedges are the modification natural to the use of clay, though when once the wedges became the standard method, the greater frequency with which clay as against stone came to be used, led to an imitation of the wedges by those who cut out the characters on stone.