It is justly remarked by Reuterdahl that no chapters of Eusebius’ History are so imperfect and unsatisfactory as those which relate to heresies, but that this is to be ascribed more to the age than to the author. A right understanding of heresies and an appreciation of any truth which they might contain was utterly impossible to men who looked upon heresy as the work of the devil, and all heretics as his chosen tools. Eusebius has been condemned by some, because he gives his information about heretics only from second hand, and quotes none of them directly; but it must be remembered that this method was by no means peculiar to Eusebius, and, moreover, it is highly probable that he did not have access to any of their works. The accounts of the heretics given by Irenæus, Hippolytus, and others would of course be preserved, but the writings of heretics themselves would be piously excluded as completely as possible from all Christian libraries, and the knowledge of them cannot have remained long in the Church. The sources upon which we have to rely at the present day for a knowledge of these heresies furnish an illustration of this. We know them almost solely through their enemies, and Eusebius knew them in the same way and very likely for the same reason.