The middle era in the Iranian linguistic history began in the 3rd or 4th century BC and continued until the 9th century AD. The Iranian languages of this era can be geographically divided into two main groups:
- The western languages
- The eastern languages
The western Middle Iranian languages are composed of:
- Parthian (Arsacid Pahlavi)
- Middle Persian
The eastern Middle Iranian languages include:
- Old Ossetic (Scytho-Sarmatian)
Parthian was spoken in the northeast and northwest of Iran. Middle Persian was spoken in the southwest. These two languages were very close linguistically.
The eastern Middle Iranian languages were quite distinct from their western counterparts. As far as their grammatical development is concerned, the eastern languages had retained their closeness to the Old Iranian languages more than the western ones.
Eastern Middle Iranian languages were all inscribed in various Aramaic alphabets. These alphabets had evolved from the Achamaenid Imperial Aramaic. They included many ideographs which were common words spelled in the original Aramaic but read in Parthian or Middle Persian.