For years, most biblical scholars followed the Augustinian hypothesis. St. Augustine (354-430) held that the Gospel of Matthew was the first to be written. The Gospel of Mark then used Matthew in the writing of his gospel. Then the Gospel of Luke followed both Matthew and Mark with his gospel. Finally, the Gospel of John was quite different from the other three. Thus, the first three were called the synoptic gospels. This is the order that you find in most bibles.
The canonization of the New Testament in the fourth century
In his Easter letter of 367 CE, Athanasius, the bishop of Alexandria, gave a list of the books that would become the 27 book New Testament canon. He actually used the word canonized, (κανονιζόμενα). The first council that accepted the present canon of the New Testament may have been the Synod of Hippo Regius in North Africa in 393 CE. In 397 CE and 419 CE, the Councils of Carthage, also in North Africa, accepted this canonical 27 number of books. These North African councils were under the authority of St. Augustine (354-430 CE), who regarded the canon as already closed. Pope Damasus I (366-384 CE) in the Council of Rome in 382 CE, issued the same biblical canon. This same Pope Damasus I commissioned St. Jerome (347-420 CE) to translate and produce the Latin Vulgate edition of the Bible around 383 CE. Thus, the fixation of the canon in the West was complete at the end of the 4th century CE.