Parenti shows that not only is history written by the winners, it's written by the upper classes of the winners - his "Gentleman Scholars". he has a wonderful quote to illustrate this which roughly is;
"Conformity of bias is taken as objectivity"From what I can gather (browsing the web) this book isn't particularly popular with many historian's but Parenti's view of Cicero and the Optimates is far closer to more recent depictions that the traditional view.
If you're a fan of Roman history give it a go. It's short, snappy and interesting.