It was spoken in northern Iran, specifically in the mountainous area in Gīlān.
Parviz Natel Khanlari listed this language as one of Iranian dialects spoken between the 9th and 13th centuries.
Istakhri, a medieval Iranian geographer, has written about this language, as did Al-Muqaddasi, a medieval Arab geographer, who wrote "they have an obscure language and they use the phoneme khe /x/ a lot.
"[1] Abū Esḥāq Ṣābī had a similar report on people in the Deylam highlands who spoke a distinct language.
One of the characteristics of this language was an added ī sound between consonants and ā (Lāhījān=Līāhījān, Amīrkā=Amīrkīā).