Theodoret of Cyrus: Haereticarum Fabularum Compendium – On Simon Magus. Here we publish a passage concerning Simon Magus from the Haereticarum Fabularum Compendium by Theodoret of Cyrus. The person of Simon Magus fades within the obscurity of legends. The published sources concerning him may be divided in three groups: the New Testament (Acts 8,5–25), the writings of the Church Fathers and the legends which arose concerning his person. All the Church Fathers present him as arch-heretic. In the introduction of this translation we will follow the way of Simon in the New Testament and in the writings of the scholars of the Early Church from his youth to his death. After having presented his life we will try to sketch out his teaching based on the available secondary sources. While Simon wrote no book from which we could reconstruct his teaching, we are acquainted with his doctrine only from the above mentioned writings. The conclusion of our introduction ends by our question concerning the possible identity of Simon of the New Testament with Simon Magus referred to by the Church Fathers.