https://en.wikipedia.org/wiki/Persian_phonology
In the modern Perso-Arabic alphabet, the short vowels /æ/, /e/ and /o/ are usually left unwritten, as is normally done in the Arabic alphabet. (See Arabic phonology § Vowels.). Historical shifts. Early New Persian inherited from Middle Persian eight vowels: three short i, a, u and five long ī, ē, ā, ō, ū (in IPA: /i a u/ and /iː eː ɑː oː uː/).It is likely that this system passed ...