Julius Caesar is often blamed for bringing about the end of the Roman Republic. I think he merely happened to be there when the Republic imploded. In 49 BC, Caesar crossed the Rubicon, a shallow river in Northern Italy, with a single legion. The river marked the border between cis-Alpine Gaul and Italy proper. Bringing armed troops into the fatherland was illegal, tantamount to treason. Caesar knew this, which is doubtless one reason he never mentions the episode in his account of the civil war that his action sparked. Nevertheless, it is worth noting that Caesar did not “cross the Rubicon” gratuitously. He had been at loggerheads with the Senate for months. Over the preceding decade, he had conquered Gaul, greatly enriching himself and the Republic. Yet Caesar had many enemies. Indeed, after a tumultuous term as consul in 59, he had originally decamped to Gaul in order to escape …