"It is well known," says Goldziher,[696] "that the earliest persecution was directed against those individuals who managed more or less adroitly to conceal under the veil of Islam old Persian religious ideas. Sometimes indeed they did not consider any disguise to be necessary, but openly set up dualism and other Persian or Manichæan doctrines, and the practices associated therewith, against the dogma and usage of Islam. Such persons were called _Zindíqs_, a term which comprises different shades of heresy and hardly admits of simple definition. Firstly, there are the old Persian families incorporated in Islam who, following the same path as the Shu‘úbites, have a _national interest_ in the revival of Persian religious ideas and traditions, and from this point of view react against the _Arabian_ character of the Muḥammadan system. Then, on the other hand, there are freethinkers, who oppose in particular the stubborn dogma of Islam, reject _positive religion_, and acknowledge only the moral law. Amongst the latter there is developed a monkish asceticism extraneous to Islam and ultimately traceable to Buddhistic influences." [Sidenote: Persecution of _Zindíqs_.] The ‘Abbásid Government, which sought to enforce an official standard of belief, was far less favourable to religious liberty than the Umayyads had been. Orthodox and heretic alike fell under its ban. While Ma’mún harried pious Sunnites, his immediate predecessors raised a hue and cry against _Zindíqs_. The Caliph Mahdí distinguished himself by an organised persecution of these enemies of the faith. He appointed a Grand Inquisitor (_Ṣáḥibu ’l-Zanádiqa_[697] or _‘Arífu ’l-Zanádiqa_) to discover and hunt them down. If they would not recant when called upon, they were put to death and crucified, and their books[698] were cut to pieces with knives.[699] Mahdí's example was followed by Hádí and Hárún al-Rashíd. Some of the ‘Abbásids, however, were less severe. Thus Khaṣíb, Manṣúr's physician, was a _Zindíq_ who professed Christianity,[700] and in the reign of Ma’mún it became the mode to affect Manichæan opinions as a mark of elegance and refinement.[701] [Sidenote: Bashshár b. Burd.]