|Lion of St. Mark, Piazza San Marco, Venice|
Raymond E. Brown's discussion of Luke as a historian in his book, Introduction to the New Testament (pp. 319-322), presents a relatively positive evaluation of Luke's historiographical credentials. Brown's estimation is based on the contents of Acts, but we'll remember that Luke-Acts are a two-part work written by the same author. Brown argues that the events in Acts are historically plausible. Acts, furthermore, contains verifiably correct details. The author, writing 30-50 years after the fact, couldn't possibly have known all of those details himself. Brown concludes, "...the author of Acts does not get bad grades for historical accuracy in the various sections of his book. Though he wrote more in a biblical style than in a classical history style, it is not ridiculous to think that the author might have been a fitting candidate for membership in the brotherhood of Hellenistic historians, even if he would never be made president of the society." (p. 322)
The author of Acts is the author of Luke. If, in Acts he does a fairly good job at preserving historical accuracy, it follows that he would have done the same in the gospel. In this light, then, we should note that Luke took over 75% of the contents of Mark into his own gospel. It's not quite correct to leap to the conclusion that because Acts is fairly accurate, therefore Mark is also fairly accurate. It is correct, however, to argue that the author of Luke-Acts was clearly concerned to preserve accurate data about the past; and to that end, he relied heavily on the Gospel of Mark for his portrayal of the Good News according to Jesus Christ. The author of Luke thought Mark was reliable. The author of Luke, furthermore, had a good sense about historical accuracy and what was reliable.
What this means is that we can't simply write Mark off as a theological mystification of the actual Jesus. If we are to question the factual reliability of his accounts, we need to have good reason. I would argue, further, that even where we can question the factuality of a given event, we can frequently rely on the underlying development of events and chronology betrayed in the event. Luke the historian trusted Mark. That trust counts for something.