"For Renaissance tyrants, 18th and 19th century generals, and 20th century dictators, Julius Caesar’s action in crossing over into Italy and marching on Rome at the head of an army represented a willingness to usurp power. ‘Crossing the Rubicon’ became so famous an event that the phrase could designate metaphorically an audacious and irreversible political step such as the invasion of Iraq in 2003. It has even been applied to sexual activity, as in the late 17th century: ‘Some Caesar pass’d my mother’s Rubicon; wou’d I had his commentaries’. Why have this and other events from Caesar’s life proved so reusable? We do well to understand it."