One of the earliest attempts at solidifying a canon was made by Marcion, circa 140 AD, who accepted only a modified version of Luke (the Gospel of Marcion) and ten of Paul's letters, while rejecting the Old Testament entirely. His canon was largely rejected by other groups of Christians, notably the proto-orthodox Christians, as was his theology, Marcionism. Adolf von Harnack, John Knox, and David Trobisch, among other scholars, have argued that the church formulated its New Testament canon partially in response to the challenge posed by Marcion.