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.