The religious evolution of Iran during the centuries from the Arab conquest to the rise of the Saljuqs was determined by a number of factors which, so far, have not been adequately isolated and analysed. This chapter identifies the politico-economical dimension of rebellions and heresies, and at the same time single out a few recurring and typical traits deserving the attention of the student of Iranian religious phenomena. It considers political and social developments of Iran by analysing their factual background before proceeding to a religious interpretation. The leader's wealth stressed by sources and the claim to Abū Muslim's treasure do not allow one to bracket this revolt together with other purely "protest" movements. The very term of Khurramdīn can in fact incorporate a number of meanings ranging from ambiguous though plausible identification with a reformed branch of new Mazdakism adjusted to Islamic pattern, to a vague sort of common denominator for a number of small sects mentioned by heresiographers.