Similarly, the heretics and rationalists, whose criticism was even more dangerous to the Church than the open violence of the State, had more in common with their opponents than we should infer from the duration and the character of the disputes which they provoked. In the background of medieval history, and developing _pari passu_ with the feud of Papacy and Empire, there was a war, of arguments and persecution, against free thought, in which the religious Orders figured as the protagonists of orthodoxy. Berengar of Tours, who challenged the doctrine of transubstantiation and so endangered the basis of the sacerdotal theory, lived in the age when a regenerated Papacy was arming for the war on secularism; it was Hildebrand himself who pronounced the final sentence on the first of the heresiarchs. The age of Henry V and of the Concordat of Worms saw the rise of a medieval Puritanism in Languedoc and Flanders. Between the Concordat of Worms and the schism of Frederic Barbarossa lies the age of Abelard,--the metaphysical free-lance who made philosophy the talk of the street-corner and the marketplace,--and of Arnold of Brescia, who demanded that the Church should be reduced to apostolic poverty. To the youthful days of Frederic II belong the Albigensian Crusade, the futile campaign of authority against Averroes and Aristotle, the heresy-hunts of volunteer inquisitors in Italy and Germany. While the same Emperor was trying conclusions with Innocent IV, the Papal Inquisition became a permanent branch of the ecclesiastical executive; and the Mendicant Orders, who supplied the inquisitors, simultaneously took upon themselves the harder task of converting the universities from the cult of Aristotle to a belief in the Christian scholasticism formulated by Albertus Magnus and Aquinas. The weapons of this interminable and many-sided controversy were as rude as the age which forged them: on the one side, coarse invective and irreverent paradox; on the other, scandalous imputations, spiritual censures, the sword, the prison, and the stake. For the medieval attitude towards heterodoxy was unflinching and uncompromising. To remain sceptical when the Church had defined was as the sin of witchcraft or idolatry. The existence of the rebel was an insult to the Most High, a menace to the salvation of the simple; he was a diseased limb of the body politic, calling for sharp surgery. And yet these nonconformists were anything but unbelievers. The free-thinkers of the schools, apart from a few obscure eccentrics, only desired to find a rational basis for the common creed or to eliminate from it certain articles which, on moral grounds and grounds of history, they stigmatised as mere interpolations. The offence of Berengar was that he attacked a dogma which had been an open question within the last two hundred years; of Abelard, that he offered his own theories on some points in regard to which the orthodox tradition was mute or inconsistent.