Avestan An: The Letter in the Avestan Alphabet

The sound is an a carried partly through the nose, the soft palate lowered so that the air escapes by both routes at once. Avestan has two signs for a nasal a and this is the first of them. The sixteen vowel letters come first in the sequence, before any consonant, and they are set out in pairs of short and long. The arrangement is inherited from nowhere. The tradition that supplied the letterforms had no such vowel series and no reason to order one this way, so the pattern comes from an analysis of the language the script was built to hold. It stands fifth in the alphabet as a whole and fifth of the sixteen vowel letters, between Avestan Aao and Avestan Aan. That position is not arbitrary.

The sequence follows a scheme, vowels before consonants and consonants by place of articulation, and each letter's place in it is a statement about the sound. The tradition calls the script din dabireh, the religion writing. It served the Avesta and very little else, and the shape of its letter list follows the sounds of that one language rather than any general requirement of writing in Sasanian Iran. The alphabet is often described as one of the most phonetically exact writing systems of the ancient world. The description is fair, and the reason for it is narrow: the script had one job, and that job rewarded precision far more than it rewarded speed.