a defined set of new scriptures; instead, the New Testament developed over time. Writings attributed to the apostles circulated among the earliest Christian communities. The Pauline epistles were circulating in collected forms by the end of the 1st century AD. Justin Martyr, in the early 2nd century, mentions the "memoirs of the Apostles", which Christians (Greek: Χριστιανός) called "gospels", and which were considered to be authoritatively equal to the Old Testament. Marcion's list Marcion of Sinope was the first Christian leader in recorded history (though later considered heretical) to propose and delineate a uniquely Christian canon (c. AD 140). This included 10 epistles from Paul, as well as an edited version of the Gospel of Luke, which today is known as the Gospel of Marcion. By doing this, he established a particular way of looking at religious texts that persists in Christian thought today. After Marcion, Christians began to divide texts into those that aligned well with the "canon" (meaning a measuring line, rule, or principle) of accepted theological thought and those that promoted heresy. This played a major role in finalizing the structure of the collection of works called the Bible. It has been proposed that the initial impetus for the proto-orthodox Christian project of canonization flowed from opposition to the list produced by Marcion. Apostolic Fathers A four-gospel canon (the Tetramorph) was asserted by Irenaeus in the following quote: "It is not possible that the gospels can be either more or fewer in number than they are. For, since there are four-quarters of the earth in which we live, and four universal winds, while the church is scattered throughout all the world, and the 'pillar and ground' of the church is the gospel and the spirit of life, it is fitting that she should have four pillars breathing out immortality on every side, and vivifying men afresh [...] Therefore the gospels are in accord with these things ... For the living creatures are quadriform and the gospel is quadriform [...] These things being so, all who destroy the form of the gospel are vain, unlearned, and also audacious; those [I mean] who represent the aspects of the gospel as being either more in number than as aforesaid, or, on the other hand, fewer." By the early 3rd century, Christian theologians like Origen of Alexandria may have been using—or at least were familiar with—the same 27 books found in