One of the most common lies you will read or hear from cultic groups is the Trinity was a 4th century invention by the Roman Emperor Constantine. For example, the Watchtower, the Jehovah’s Witnesses governing body, states, “FACT: The Trinitarian dogma is a late fourth-century invention.”1
One of the clearest references to the Triune nature of God without using the word Trinity is found in the writings of Ignatius. He was the Bishop of Antioch during the reign of the Emperor Trajan (98–117 A.D.) In addition to being a martyr for the faith, he was taught by the Apostle John. On the way to his death in Rome, he wrote a letter to the church at Magnesia where he laid out the different persons of the Trinity 2 3:
Study, therefore, to be established in the doctrines of the Lord and the apostles, that so all things, whatsoever ye do, may prosper both in the flesh and spirit; in faith and love; in the Son, and in the Father, and in the Spirit; in the beginning and in the end; with your most admirable bishop, and the well-compacted spiritual crown of your presbytery, and the deacons who are according to God. Be ye subject to the bishop, and to one another, as Jesus Christ to the Father, according to the flesh, and the apostles to Christ, and to the Father, and to the Spirit; that so there may be a union both fleshly and spiritual.4
Ignatius clearly believed in one God, yet referenced different persons who comprised God. He stressed how his church must submit to the doctrines of “the Lord and the apostles” so they would prosper in unity just as the Father, Son, and Spirit are in union.
Early church father and theologian, Quintus Septimius Florens Tertullian, used the word Trinity in his writings. He was born in the city of Carthage in North Africa and lived between 160 to 225 A.D. He became a convert to Christianity sometime in his late thirties. He served as an elder or minister at his local church. Tertullian was known to have had a “superior education, including literary, rhetorical, and legal training, and instruction in Greek and Latin.”5
The term Trinity was actually first used by Tertullian, who coined the Latin word “trinitas” to express the unique intradivine relationship among the three persons of the Godhead.6 According to the book, Who’s Who in Christian History, “Tertullian’s use of the Latin trinitas (was) the first application of the term trinity to Deity.”7 Thus, it would be fallacious to say that the Trinity is pagan if one of the most prolific Christian minds coined the term long before the 4th century.
Another early Christian who taught God was a Trinity was Dionysius. He was the Bishop of Rome from 259-260 A.D. He held to a Trinitarian view of God and sought to combat Sabellianism (which states that God exists in three modes or manifestations and not three Persons), Tritheism (meaning three different gods make up the Trinity), and subordinationism (which means the Son is not eternal or divine and not equal to the Father) in his writings.8 In his work, Against the Sabellians, he explained how God was not made up of three deities but of three persons. He believed that the Trinity was a doctrine explicitly taught in Scripture,9 “For these indeed rightly know that the Trinity is declared in the divine Scripture, but that the doctrine that there are three gods is neither taught in the Old nor in the New Testament.”10 In addition, he explained how three persons comprise the Godhead,
That admirable and divine unity, therefore, must neither be separated into three divinities, nor must the dignity and eminent greatness of the Lord be diminished by having applied to it the name of creation, but we must believe on God the Father Omnipotent, and on Christ Jesus His Son, and on the Holy Spirit. Moreover, that the Word is united to the God of all, because He says, “I and the Father are one;” and, “I am in the Father, and the Father is in Me.” Thus doubtless will be maintained in its integrity the doctrine of the divine Trinity, and the sacred announcement of the monarchy.11
This is yet another example of an early Christian that taught the Trinity and condemned all other views as heretical.
In summary, it can be easily demonstrated through multiple early church fathers that the doctrine of the Trinity was not a late fourth-century invention. The doctrine and term was in use at least two centuries earlier. To declare otherwise would be a false assertion.
 JW.ORG. The Watchtower November 2009. Myth 4: God Is a Trinity. Accessed June 11, 2016 at https://www.jw.org/en/publications/magazines/wp20091101/myth-god-is-a-trinity/#?insight[search_id]=e6a2b140-75da-41c7-82aa-8aa8289af8e4&insight[search_result_index]=3
 J. Christian Wilson, “Ignatius of Antioch,” ed. David Noel Freedman, Allen C. Myers, and Astrid B. Beck, Eerdmans Dictionary of the Bible (Grand Rapids, MI: W.B. Eerdmans, 2000), 627.
 Alexander Roberts, James Donaldson, and A. Cleveland Coxe, eds., “Introductory Note to the Epistle of Ignatius to the Ephesians,” in The Apostolic Fathers with Justin Martyr and Irenaeus, vol. 1, The Ante-Nicene Fathers (Buffalo, NY: Christian Literature Company, 1885), 45.
 Biblehub.com. The Epistle of Ignatius to the Magnesians-Ignatius. Accessed on June 12,2016 at http://biblehub.com/library/ignatius/the_epistle_of_ignatius_to_the_magnesians/chapter_xiii_be_established_in_faith.htm
 K.J. Bryer, “Tertullian,” ed. J.D. Douglas and Philip W. Comfort, Who’s Who in Christian History (Wheaton, IL: Tyndale House, 1992), 665.
 D. Larry Gregg, “Trinity,” ed. David Noel Freedman, Allen C. Myers, and Astrid B. Beck, Eerdmans Dictionary of the Bible (Grand Rapids, MI: W.B. Eerdmans, 2000), 1336.
 K.J. Bryer, ibid
 Samuel Macauley Jackson, ed., The New Schaff-Herzog Encyclopedia of Religious Knowledge: Embracing Biblical, Historical, Doctrinal, and Practical Theology and Biblical, Theological, and Ecclesiastical Biography from the Earliest Times to the Present Day (New York; London: Funk & Wagnalls, 1908–1914), 52.
 Schaff,Philip. Dionysius Alexandrinus Archiepiscopus – Against the Sabellians. Accessed June 12, 2016 at http://www.documentacatholicaomnia.eu/03d/0190-0264,_Dionysius_Alexandrinus,_Against_the_Sabellians_[Schaff],_EN.pdf