Actually, unlike Trinitarianism, both Arian and Sabellian or modalistic theology resulted in large measure from the influence of pagan thought upon Christianity. This fact is the affirmation of real historians quoted in context, rather than the creation of quotations slashed and burned from their contexts or from the assorted weirdos cited by the Watchtower Society. “[The system of] Sabellius . . . sprung out of Judaizing and Gnostic tendencies which were indigenous to Egypt. . . . [A] pantheistic tendency [also characterizes] Sabellianism as a whole. . . . Kindred ideas are also found in Pythagoreanism.” “[O]pposition to the Incarnate Word, when he really appeared, seemed to have predisposed [modalists, here discussed under the label of Monarchians] to accept a heathen philosophy, and to represent the Logos as Philo did as the manifest God not personally distinct from the concealed Deity. This error found its way into Christianity through the Gnostics, who were largely indepted to the Platonic school of Alexandria. . . . Sabellianism [in part is] found even in the later schools of gnostics, and the later Sabellianism approached to an emanation theory. . . . The leading tenet of the Monarchians [modalists] thus appears to have been introduced into Christianity principally through the Alexandrian Jews and the Gnostics. It may also have been derived immediately from heathen philosophers. . . . [T]he Monarchians who identified the Son with the Father and admitted at most only a modal trinity, a threefold mode of revelation . . . proceeded, at least in part, from pantheistic preconceptions, and approached the ground of Gnostic docetism.” Modalism is a concept which mixes Christianity and paganism.
Similarly, “Arius . . . was following . . . a path inevitably traced for him by the Middle Platonist preconceptions he had inherited,” since “the impact of Platonism reveals itself in . . . thoroughgoing subordinationism.” The Arian view of the incarnation of Christ “took as its premis[e] [a] Platonic conception.”
Examining the history of ancient Christianity, one notes that no physical evidence exists of Arius, Sabellius, or the disciples of either of these heretics affirming and disperaging Trinitarian doctrine as derived from paganism, while testimony from ancient Christiandom affirms that modalist and Unitarian heretics derived their ideas from paganism. The Trinitarian Tertullian spoke strongly against the adoption of pagan philosophy, mentioning that “Plato has been the caterer to all these heretics” and speaks of “doctrines which the heretics borrow from Plato.” He writes, “Indeed heresies are themselves instigated by [pagan] philosophy.” Specifically speaking against the Unitarian heresy, Athanasius declared, “when the unsound nature of their phrases had been exposed at that time, and they were henceforth open to the charge of irreligion, that they proceeded to borrow of the Greeks [pagan philosophy] . . . so unblushing are they in their irreligion, so obstinate in their blasphemies against the Lord. . . . they are contentious, as elsewhere, for unscriptural positions . . . [their language, namely, adopting the term “Unoriginate” for God over “Father,” is] of the Greeks who know not the Son.” Ambrose wrote, “Let us now see how far Arians and pagans do differ. . . . The pagans assert that their gods began to exist once upon a time; the Arians lyingly declare that Christ began to exist in the course of time. Have they not all dyed their impiety in the vats of philosophy?” The evidence from patristic writers affirms that the doctrines of Arianism, Sabellianism, and other heresies were influenced by paganism. No extant ancient writer affirms that the Trinity was borrowed from pagan philosophy. Who is more likely to be correct on the development of Trinitarian theology—those who lived in the first centuries of Christianity, or the wackos quoted by modern Arians and Sabellians who lived a millenium and a half after the end of the ancient church period?
Indeed, even the pagans testified that the Christians believed that the Lord Jesus Christ was God. For example, the Roman official Pliny the Younger wrote to the the Roman emperor Trajan c. A. D. 112: “I ask them if they are Christians. If they admit this, I ask them the question again a second and third time, threatening them with the death sentence if they persist. . . . But they declared that their only crime or error was that they used to meet regularly before daybreak on an appointed day, and to sing a hymn to Christ as to God, and to bind themselves by an oath not to commit any crime, but to abstain from theft, robbery, adultery or breach of trust, and not to deny a deposit when this was required” (Pliny, Letters 10.96, in The Letters of Pliny, 2 vols., trans. William Melmoth. Cambridge: Harvard University Press, 1915, 2:403ff.).
Anti-Trinitiarian affirmations that the Trinity is derived from paganism are radically anti-historical--just as they are radically anti-Biblical.
 “Sabellius” in the Cyclopedia of Biblical, Theological, and Ecclesiastical Literature, John McClintock & James Strong, vol. 9. Rio, WI: AGES Digital Software Library, 2006, elec. acc.
Of course, this affirmation does not deny that Arius or Sabellius, added particular twists of their own to their pagan patrimony (so that, e. g., the article just quoted while affirming Sabellius’ pagan heritage, can also speak of his “originality.”)
 “Monarchianism,” Cyclopedia of Biblical, Theological, and Ecclesiastical Literature, McClintock & Strong, vol. 6.
 pg. 231, Early Christian Doctrines, J. N. D. Kelly. San Francisco, CA: HarperCollins, 1978 (5th rev. ed).
 pg. 131, Early Christian Doctrines, Kelly. The quote specifically speaks of the theology of the heretic and (less radical, but still) Arian precursor, Origin.
 pg. 281, Early Christian Doctrines, Kelly. Other heretics also adopted a Platonized view of the incarnation.
 Chapter 23, A Treatise on the Soul. (Church Fathers — The Ante-Nicene Fathers, ed. Alexander Roberts & James Donaldson. elec. acc. Accordance Bible Software, ver. 1.1. This is the edition employed for quotations from patristic writers unless otherwise specified.). It would be very strange for Tertullian to condemn various heretics for deriving their doctrines from Plato if he himself derived his Trinitarianism from Plato.
 Chapter 7, The Prescription Against Heretics.
 Defence of the Nicene Definition (De Decretis), 28, 31.
 Exposition of the Christian Faith, Ambrose. Book 1:13:85.