History of the Doctrine Concerning the Nature of God
In the Early Centuries of Christianity
Monarchianism was also called sabellianism, from sabellius, its mostfamous exponent  who was teaching in rome during the later part of hislife, about 215 a.d. 
God appeared to men and made himself known as father, as son, as the holyspirit. Both things being true, the obvious solution is that the trinity isone of manifestation. God is like an actor on a greek stage; he is able totake different parts at different times by putting on a new mask or face (thisis the literal and original meaning of the greek word for person, “prosopon”,which was applied by sabellius to the roles of father, son and spirit). Hewas influenced, i believe, at this point by noting (a) that according to thefourth gospel the holy spirit does not come until the son is glorified.
Sabellius used analogies, commonly employed by trinitarians todemonstrate how three can be one, to prove that the three manifestations are,in reality, one person. The one sun has roundness, heat, and light; but thereis only one sun. The one man has body, soul, and spirit; but there is onlyone person. So god might manifest himself as father, son,and holy spirit,
But still be only one person.
Dr. Lowry acknowledges that the sabellian view “left a permanent impressupon subsequent trinitarian theology. It taught that the persons of the trinity were entirely equal and that Christ is fully god.” 
The dominant sabellian tendency battled to defend itself against thenewer logos-christology doctrine. Sabellius said that father, son, and Holy Spirit are each a “prosopon” (manifestation) of one god. Sabellius, thoughsoon excommunicated at rome had a very large following. His absolute identification of father, son, and holy spirit was rejected by the roman
Bishop, but it implied an equality which ultimately, as in augustine,triumphed over the subordination of son and spirit, characteristic of thelogos-christology both of tertullian and athanasius. 
(notice that the doctrine of the trinity (“as in augustine”) accepted theimplied equality of the father and son of monarchianism instead of the logos-christology theory of subordination of the son to the father, of tertullian –and even athanasius, whose name is associated with the original nicean creedof the trinity!)
Kallistos had excommunicated Sabellius, the strong defender of monarchianism, and strong pressure was being brought to bear by government and church officials to wipe out the teaching that God was one person in three manifestations. Dionysius, head of Catechetical school in Alexandria, and Bishiop of that city around the middle of the 3rd century still founds a bellianism very influential in his diocese and preached against it. In fact monarchianism continued until the 6th century, being the only viewpointallowed in the country that Sabellius had fled to, in earlier days.