But indeed, besides the treatises and letters of Irenaeus that have been mentioned, there is current a most necessary and very brief, and especially most necessary, discourse of his, entitled 「Concerning Knowledge」; and another, which he dedicated to a brother named Marcianus, 「In Demonstration of the Apostolic Preaching」; and a certain book of various discourses, in which he mentions the Epistle to the Hebrews and the so-called Wisdom of Solomon, citing certain passages from them. Such, then, are the works of Irenaeus that have come to our knowledge. And when Commodus had brought his rule to an end after thirteen years, and Pertinax had survived not even six full months after the death of Commodus, the emperor Severus held power.