Doctrine was further refined by a series of influential theologians and teachers, known collectively as the Church Fathers.[37] From the year 100 onward, proto-orthodox teachers like Ignatius of Antioch and Irenaeus defined Catholic teaching in stark opposition to other things, such as Gnosticism.[38] Teachings and traditions were consolidated under the influence of theological apologists such as Pope Clement I, Justin Martyr and Augustine of Hippo.[39]