According to tradition Mark gathered quotes and events from Jesus when Peter spoke. As such and because Mark was not a witness himself of these events, the result is not very chronological. Nevertheless Mark did a good job, because Matthew who was a witness follows him to a very large extent, but he did not change a lot regarding to the chronology either. But this was confusing at some points, therefor Luke says in the first four verses of his report, that he went through the previous written material (as well as adding new things from witnesses) to put it into a consistent and chronological order. One of the problems with Mark is his chapter 13 and Matthew's chapter 24. Quotes from Jesus about the destruction of Jerusalem and of the second coming of Christ were mixed together. Therefore Luke splits those into two. Chapter 17 is only about the coming of Christ and chapter 21 first is about the destruction of Jerusalem and then switches to Jesus' second coming. ...