"Valentinus and his followers derived the principles of their system from the Heathen; the names only are changed."

Irenaeus says in the Preface to his "Against Heresies", that among all the heresies and heretics, the ones he is most concerned with are Valentinus and his followers. In Book II, Chapter 14, reproduced below, Irenaeus insists that the ideas of the Valentinians were not merely "derived ... from the Heathen, the names only are changed," but, moreover, Valentinianism is, according to Irenaeus, especially indebted to "those who were ignorant of God, and who are termed philosophers."

It is worth remembering in this context that not only did Dante place Epicurus in the Sixth Ring of Hell, the place dedicated to Heretics, but Pope Leo X, in his Bull of excommunication, compared Luther to Porphyry.

Here is Book II, Chapter 14 in its entirety, taken from http://www.newadvent.org/fathers/0103214.htm.

Against Heresies (Book II, Chapter 14)

Valentinus and his followers derived the principles of their system from the Heathen; the names only are changed.
 
1. Much more like the truth, and more pleasing, is the account which Antiphanes, one of the ancient comic poets, gives in his Theogony as to the origin of all things. For he speaks Chaos as being produced from Night and Silence; relates that then Love sprang from Chaos and Night; from this again, Light; and that from this, in his opinion, were derived all the rest of the first generation of the gods. After these he next introduces a second generation of gods, and the creation of the world; then he narrates the formation of mankind by the second order of the gods. These men (the heretics), adopting this fable as their own, have ranged their opinions round it, as if by a sort of natural process, changing only the names of the things referred to, and setting forth the very same beginning of the generation of all things, and their production. In place of Night and Silence they substitute Bythus and Sige; instead of Chaos, they put Nous; and for Love (by whom, says the comic poet, all other things were set in order) they have brought forward the Word; while for the primary and greatest gods they have formed the Æons; and in place of the secondary gods, they tell us of that creation by their mother which is outside of the Pleroma, calling it the second Ogdoad. They proclaim to us, like the writer referred to, that from this (Ogdoad) came the creation of the world and the formation of man, maintaining that they alone are acquainted with these ineffable and unknown mysteries. Those things which are everywhere acted in the theatres by comedians with the clearest voices they transfer to their own system, teaching them undoubtedly through means of the same arguments, and merely changing the names.

2. And not only are they convicted of bringing forward, as if their own [original ideas], those things which are to be found among the comic poets, but they also bring together the things which have been said by all those who were ignorant of God, and who are termed philosophers; and sewing together, as it were, a motley garment out of a heap of miserable rags, they have, by their subtle manner of expression, furnished themselves with a cloak which is really not their own. They do, it is true, introduce a new kind of doctrine, inasmuch as by a new sort of art it has been substituted [for the old]. Yet it is in reality both old and useless, since these very opinions have been sewed together out of ancient dogmas redolent of ignorance and irreligion. For instance, Thales of Miletus affirmed that water was the generative and initial principle of all things. Now it is just the same thing whether we say water or Bythus. The poet Homer, again, held the opinion that Oceanus, along with mother Tethys, was the origin of the gods: this idea these men have transferred to Bythus and Sige. Anaximander laid it down that infinitude is the first principle of all things, having seminally in itself the generation of them all, and from this he declares the immense worlds [which exist] were formed: this, too, they have dressed up anew, and referred to Bythus and their Æons. Anaxagoras, again, who has also been surnamed Atheist, gave it as his opinion that animals were formed from seeds falling down from heaven upon earth. This thought, too, these men have transferred to the seed of their Mother, which they maintain to be themselves; thus acknowledging at once, in the judgment of such as are possessed of sense, that they themselves are the offspring of the irreligious Anaxagoras.

3. Again, adopting the [ideas of] shade and vacuity from Democritus and Epicurus, they have fitted these to their own views, following upon those [teachers] who had already talked a great deal about a vacuum and atoms, the one of which they called that which is, and the other that which is not. In like manner, these men call those things which are within the Pleroma real existences, just as those philosophers did the atoms; while they maintain that those which are without the Pleroma have no true existence, even as those did respecting the vacuum. They have thus banished themselves in this world (since they are here outside of the Pleroma) into a place which has no existence. Again, when they maintain that these things [below] are images of those which have a true existence [above], they again most manifestly rehearse the doctrine of Democritus and Plato. For Democritus was the first who maintained that numerous and diverse figures were stamped, as it were, with the forms [of things above], and descended from universal space into this world. But Plato, for his part, speaks of matter, and exemplar, and God. These men, following those distinctions, have styled what he calls ideas, and exemplar, the images of those things which are above; while, through a mere change of name, they boast themselves as being discoverers and contrivers of this kind of imaginary fiction.

4. This opinion, too, that they hold the Creator formed the world out of previously existing matter, both Anaxagoras, Empedocles, and Plato expressed before them; as, forsooth, we learn they also do under the inspiration of their Mother. Then again, as to the opinion that everything of necessity passes away to those things out of which they maintain it was also formed, and that God is the slave of this necessity, so that He cannot impart immortality to what is mortal, or bestow incorruption on what is corruptible, but every one passes into a substance similar in nature to itself, both those who are named Stoics from the portico (στοὰ), and indeed all that are ignorant of God, poets and historians alike, make the same affirmation. Those [heretics] who hold the same [system of] infidelity have ascribed, no doubt, their own proper region to spiritual beings—that, namely, which is within the Pleroma, but to animal beings the intermediate space, while to corporeal they assign that which is material. And they assert that God Himself can do no otherwise, but that every one of the [different kinds of substance] mentioned passes away to those things which are of the same nature [with itself].

5. Moreover, as to their saying that the Saviour was formed out of all the Æons, by every one of them depositing, so to speak, in Him his own special flower, they bring forward nothing new that may not be found in the Pandora of Hesiod. For what he says respecting her, these men insinuate concerning the Saviour, bringing Him before us as Pandoros (All-gifted), as if each of the Æons had bestowed on Him what He possessed in the greatest perfection. Again, their opinion as to the indifference of [eating of] meats and other actions, and as to their thinking that, from the nobility of their nature, they can in no degree at all contract pollution, whatever they eat or perform, they have derived it from the Cynics, since they do in fact belong to the same society as do these [philosophers]. They also strive to transfer to [the treatment of matters of] faith that hairsplitting and subtle mode of handling questions which is, in fact, a copying of Aristotle.

6. Again, as to the desire they exhibit to refer this whole universe to numbers, they have learned it from the Pythagoreans. For these were the first who set forth numbers as the initial principle of all things, and [described] that initial principle of theirs as being both equal and unequal, out of which [two properties] they conceived that both things sensible and immaterial derived their origin. And [they held] that one set of first principles gave rise to the matter [of things], and another to their form. They affirm that from these first principles all things have been made, just as a statue is of its metal and its special form. Now, the heretics have adapted this to the things which are outside of the Pleroma. The [Pythagoreans] maintained that the principle of intellect is proportionate to the energy wherewith mind, as a recipient of the comprehensible, pursues its inquiries, until, worn out, it is resolved at length in the Indivisible and One. They further affirm that Hen— that is, One— is the first principle of all things, and the substance of all that has been formed. From this again proceeded the Dyad, the Tetrad, the Pentad, and the manifold generation of the others. These things the heretics repeat, word for word, with a reference to their Pleroma and Bythus. From the same source, too, they strive to bring into vogue those conjunctions which proceed from unity. Marcus boasts of such views as if they were his own, and as if he were seen to have discovered something more novel than others, while he simply sets forth the Tetrad of Pythagoras as the originating principle and mother of all things.

7. But I will merely say, in opposition to these men — Did all those who have been mentioned, with whom you have been proved to coincide in expression, know, or not know, the truth? If they knew it, then the descent of the Saviour into this world was superfluous. For why [in that case] did He descend? Was it that He might bring that truth which was [already] known to the knowledge of those who knew it? If, on the other hand, these men did not know it, then how is it that, while you express yourselves in the same terms as do those who knew not the truth, you boast that yourselves alone possess that knowledge which is above all things, although they who are ignorant of God [likewise] possess it? Thus, then, by a complete perversion of language, they style ignorance of the truth knowledge: and Paul well says [of them,] that [they make use of] novelties of words of false knowledge. For that knowledge of theirs is truly found to be false. If, however, taking an impudent course with respect to these points, they declare that men indeed did not know the truth, but that their Mother, the seed of the Father, proclaimed the mysteries of truth through such men, even as also through the prophets, while the Demiurge was ignorant [of the proceeding], then I answer, in the first place, that the things which were predicted were not of such a nature as to be intelligible to no one; for the men themselves knew what they were saying, as did also their disciples, and those again succeeded these. And, in the next place, if either the Mother or her seed knew and proclaimed those things which were of the truth (and the Father is truth), then on their theory the Saviour spoke falsely when He said, No one knows the Father but the Son, Matthew 11:27 unless indeed they maintain that their seed or Mother is No-one.

8. Thus far, then, by means of [ascribing to their Æons] human feelings, and by the fact that they largely coincide in their language with many of those who are ignorant of God, they have been seen plausibly drawing a certain number away [from the truth]. They lead them on by the use of those [expressions] with which they have been familiar, to that sort of discourse which treats of all things, setting forth the production of the Word of God, and of Zoe, and of Nous, and bringing into the world, as it were, the [successive] emanations of the Deity. The views, again, which they propound, without either plausibility or parade, are simply lies from beginning to end. Just as those who, in order to lure and capture any kind of animals, place their accustomed food before them, gradually drawing them on by means of the familiar aliment, until at length they seize it, but, when they have taken them captive, they subject them to the bitterest of bondage, and drag them along with violence wherever they please; so also do these men gradually and gently persuading [others], by means of their plausible speeches, to accept of the emission which has been mentioned, then bring forward things which are not consistent, and forms of the remaining emissions which are not such as might have been expected. They declare, for instance, that [ten] Æons were sent forth by Logos and Zoe, while from Anthropos and Ecclesia there proceeded twelve, although they have neither proof, nor testimony, nor probability, nor anything whatever of such a nature [to support these assertions]; and with equal folly and audacity do they wish it to be believed that from Logos and Zoe, being Æons, were sent forth Bythus and Mixis, Ageratos and Henosis, Autophyes and Hedone, Acinetos and Syncrasis, Monogenes and Macaria. Moreover, [as they affirm,] there were sent forth, in a similar way, from Anthropos and Ecclesia, being Æons, Paracletus and Pistis, Patricos and Elpis, Metricos and Agape, Ainos and Synesis, Ecclesiasticus and Macariotes, Theletos and Sophia.

9. The passions and error of this Sophia, and how she ran the risk of perishing through her investigation [of the nature] of the Father, as they relate, and what took place outside of the Pleroma, and from what sort of a defect they teach that the Maker of the world was produced, I have set forth in the preceding book, describing in it, with all diligence, the opinions of these heretics. [I have also detailed their views] respecting Christ, whom they describe as having been produced subsequently to all these, and also regarding Soter, who, [according to them,] derived his being from those Æons who were formed within the Pleroma. But I have of necessity mentioned their names at present, that from these the absurdity of their falsehood may be made manifest, and also the confused nature of the nomenclature they have devised. For they themselves detract from [the dignity of] their Æons by a multitude of names of this sort. They give out names plausible and credible to the heathen, [as being similar] to those who are called their twelve gods, and even these they will have to be images of their twelve Æons. But the images [so called] can produce names [of their own] much more seemly, and more powerful through their etymology to indicate divinity [than are those of their fancied prototypes].