Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 12. The Development of Catholic Theology in Conflict with Heresy” Sections 137-158, Loc. 18758-20235.
§ 150. Antitrinitarians. First class: The Alogi, Theodotus, Artemon, Paul of Samosata.
Schaff observes that the doctrine of the Trinity was well articulated primarily due to controversies of the third century, in which various antitrinitarians arose, normally called Monarchians or Unitarians. Both titles imply the Godhead existing in only one person. Schaff cautions that “we must carefully distinguish among the two opposite classes: the rationalistic or dynamic Monarchians, who denied the divinity of Christ, or explained it as a mere “power”. . . and the patripassian or modalistic Monarchians, who identified the Son with the Father, and admitted at most only a modal trinity, that is a threefold mode of revelation, but not a tripersonality” (Schaff 2014, Loc. 19668). The first, dealt with in this section, was refuted in Christianity but arose outside of the Church, particularly in Islam and in the Eastern Unitarian sects. In essence, Schaff finds, the first class of Monarchians saw Christ merely as a man, but endowed with special power of the Holy Spirit.
Among the first class Monarchians Schaff classes the Alogi, who rejected the idea of Christ as the Logos. They also rejected the Apocalypse as something of no use (Schaff 2014, Loc. 19682). The Theodotians, another group, arose in Byzantium. Theodotus denied Christ in a time of persecution, saying he was only a man, but later said he considered “him to be the supernaturally begotten Messiah” (Schaff 2014, Loc. 19689). Theodotus was excommunicated between 192 and 202. His followers selected another bishop afterwards. The followers of Artemon were a bit later, after 202. Artemon considered the divinity of Christ to be an innovation rather than a tenet held by Christians from the outset. His followers were very enthusiastic about mathematics and pagan Greek philosophers (Schaff 2014, Loc. 19695). Finally, Paul of Samosata, bishop of Antioch after 260, considered the Son and the Holy Spirit “merely powers of God” (Schaff 2014, Loc. 19702). He was accused of both heresy and other character flaws before being deposed in 268 or 269, after which time the first class Monarchians largely declined (Schaff 2014, Loc. 19709).