At first, when his friends would have persuaded him to stand to be tribune of the people, he thought it undesirable; for that the power of so great an office ought to be reserved, as the strongest medicines, for occasions of the last necessity. But afterwards in a vacation time, as he was going, accompanied with his books and philosophers, to Lucania, where he had lands with a pleasant residence, they met by the way a great many horses, carriages, and attendants, of whom they understood, that Metellus Nepos was going to Rome, to stand to be tribune of the people. Hereupon Cato stopped, and after a little pause, gave orders to return back immediately; at which the company seeming to wonder, "Don't you know,"said he, "how dangerous of itself the madness of Metellus is? and now that he comes armed with the support of Pompey, he will fall like lightning on the state, and bring it to utter disorder; therefore this is no time for idleness and diversion, but we must go and prevent this man in his designs, or bravely die in defence of our liberty."Nevertheless, by the persuasion of his friends, he went first to his country-house, where he stayed but a very little time, and then returned to town.
He arrived in the evening, and went straight the next morning to the forum, where he began to solicit for the tribuneship, in opposition to Metellus. The power of this office consists rather in controlling than performing any business; for though all the rest except any one tribune should be agreed, yet his denial or intercession could put a stop to the whole matter. Cato, at first, had not many that appeared for him; but as soon as his design was known, all the good and distinguished persons of the city quickly came forward to encourage and support him, looking upon him, not as one that desired a favour of them, but one that proposed to do a great favour to his country and all honest men; who had many times refused the same office, when he might have had it without trouble, but now sought it with danger, that he might defend their liberty and their government. It is reported that so great a number flocked about him that he was like to be stifled amidst the press, and could scarce get through the crowd. He was declared tribune, with several others, among whom was Metellus.
When Cato was chosen into this office, observing that the election of consuls was become a matter of purchase, he sharply rebuked the people for this corruption, and in the conclusion of his speech protested he would bring to trial whomever he should find giving money, making an exception only in the case of Silanus, on account of their near connection, he having married Servilia, Cato's sister.
He therefore did not prosecute him, but accused Lucius Murena, who had been chosen consul by corrupt means with Silanus. There was a law that the party accused might appoint a person to keep watch upon his accuser, that he might know fairly what means he took in preparing the accusation. He that was set upon Cato by Murena, at first followed and observed him strictly, yet never found him dealing any way unfairly or insidiously, but always generously and candidly going on in the just and open methods of proceeding. And he so admired Cato's great spirit, and so entirely trusted to his integrity, that meeting him in the forum, or going to his house, he would ask him if he designed to do anything that day in order to the accusation, and if Cato said no, he went away, relying on his word. When the cause was pleaded Cicero, who was then consul and defended Murena, took occasion to be extremely witty and jocose, in reference to Cato, upon the Stoic philosophers, and their paradoxes, as they call them, and so excited great laughter among the judges; upon which Cato, smiling, said to the standers-by, "What a pleasant consul we have, my friends." Murena was acquitted, and afterwards showed himself a man of no ill-feeling or want of sense; for when he was consul, he always took Cato's advice in the most weighty affairs and, during all the time of his office, paid him much honour and respect. Of which not only Murena's prudence, but also Cato's own behaviour, was the cause; for though he were terrible and severe as to matters of justice, in the senate, and at the bar, yet after the thing was over his manner to all men was perfectly friendly and humane.
Before he entered on the office of tribune, he assisted Cicero, at that time consul, in many contests that concerned his office, but most especially in his great and noble acts at the time of Catiline's conspiracy; which owed their last successful issue to Cato. Catiline had plotted a dreadful and entire subversion of the Roman state by sedition and open war, but being convicted by Cicero, was forced to fly the city. Yet Lentulus and Cethegus remained, with several others, to carry on the same plot; and blaming Catiline, as one that wanted courage, and had been timid and petty in his designs, they themselves resolved to set the whole town on fire, and utterly to overthrow the empire, rousing whole nations to revolt and exciting foreign wars. But the design was discovered by Cicero (as we have written in his life), and the matter brought before the senate.
Silanus, who spoke first, delivered his opinion, that the conspirators ought to suffer the last of punishments, and was therein followed by all who spoke after him; till it came to Caesar, who being an excellent speaker, and looking upon all changes and commotions in the state as materials useful for his own purposes, desired rather to increase than extinguish them; and standing up, he made a very merciful and persuasive speech, that they ought not to suffer death without fair trial according to law, and moved that they might be kept in prison. Thus was the house almost wholly turned by Caesar, apprehending also the anger of the people; insomuch that even Silanus retracted, and said he did not mean to propose death, but imprisonment, for that was the utmost a Roman could suffer.