In The Grass Crown, Colleen McCullough has an elaborate story about Marius Junior having killed his commander, the consul L. Porcius Cato, during a battle, and the consequent machinations by Marius Senior to get young Marius out of this mess, let alone the “heroics” of young Caesar. This of course makes for a good story inasmuch as it puts Cinna into debt to Marius, thus preparing their future sordid cooperation.
Arthur Keaveney, in Rome And The Unification Of Italy, p. 152, brings up the subject. He writes that it may well be that Cato, who had disciplinary problems with his troops, had been murdered by his unruly troops in the battle in which he was defeated by the Marsi. Keaveney then continues to say that whether the assassin was young Marius – who is said to have been incensed about the consul disparaging his father – would always remain a subject of debate; however that prominence should be given to the “savage nature” of young Marius and the family’s notorious touchiness about its “rights,” when considering the issue. He talks of “according to one story,” but his endnote and list of sources relates to more than just the murder, so I don't know who the source would be, except to say that is is not any of the ancient sources that I have access to.
A note on Keaveney’s book: It's a thorough and fascinating evaluation of the history of the unification of Italy, from early in the second century B.C. to Sulla’s final affirmation of the general franchise. However, it pre-supposes a certain knowledge by the reader of the chain of events and the major players ,and magistracies during crucial years.
