Then there was Montanism and Donatism and Docetism and Apollinarianism... There is no end of heretical “isms.” But the major heresy of the church’s first four centuries was Arianism.

So did the likes of Clement, Ignatius, Justin Martyr, Irenaeus, Origen, Tertullian, John of Chrysodom, Jerome and Augustine do fierce moral and intellectual battle with Arianism, Gnosticism, Docetism, ...