Gospel of Thomas in the late 2nd century that "since there are four quarters of the earth ... it is fitting that the church should have four pillars ... the four Gospels" ("Against Heresies", 3.11.8), and then shortly thereafter made the first known quotation from a fourth gospel—the canonical version of the Gospel of John. The late 2nd-century Muratorian fragment also recognizes only the three synoptic gospels and John. Bible scholar Bruce Metzger wrote regarding the formation of the New Testament canon, "Although the fringes of the emerging canon remained unsettled for generations, a high degree of unanimity concerning the greater part of
Synoptic Gospels that have been fulfilled among us, just as they were handed on to us by those who from the beginning were eyewitnesses and servants of the word, I too decided, after investigating everything carefully from the very first, to write an orderly account for you, most excellent Theophilus, so that you may know the truth concerning the things about which you have been instructed. The "synoptic problem" is the question of the specific literary relationship among the three synoptic gospels—that is, the question as to the source or sources upon which each synoptic gospel depended when it was written. The