C. Julius Caesar, Gallic War

Then at length Liscus, moved by Caesar's speech, discloses what he had hitherto kept secret:-that there are some whose influences with the people is very great, who, though private men, have more power than the magistrates themselves: that these by seditions and violent language are deterring the populace from contributing the corn which they ought to supply; [by telling them] that, if they can not any longer retain the supremacy of Gaul, it were better to submit to the government of Gauls than of Romans, nor ought they to doubt that, if the Romans should overpower the Helvetii, they would wrest their freedom from the Aedui together with the remainder of Gaul. By these very men, [said he], are our plans and whatever is done in the camp, disclosed to the enemy; that they could not be restrained by him: nay more, he was well aware, that though compelled by necessity, he had disclosed the matter to Caesar, at how great a risk he had done it; and for that reason, he had been silent as long as he could."