Niccolò Machiavelli
Discourses on the First Decade of Titus Livius (Chap. 1.3) (English version)
Of the Accidents which led in Rome to the creation of Tribunes of the People; whereby the Republic was made more perfect.

They who lay the foundations of a State and furnish it with laws must, as is shown by all who have treated of civil government, and by examples of which history is full, assume that 'all men are bad, and will always, when they have free field, give loose to their evil inclinations; and that if these for a while remain hidden, it is owing to some secret cause, which, from our having no contrary experience, we do not recognize at once, but which is afterwards revealed by Time, of whom we speak as the father of all truth.

In Rome, after the expulsion of the Tarquins, it seemed as though the closest union prevailed between the senate and the commons, and that the nobles, laying aside their natural arrogance, had learned so to sympathize with the people as to have become supportable by all, even of the humblest rank. This dissimulation remained undetected, and its causes concealed, while the Tarquins lived; for the nobles dreading the Tarquins, and fearing that the people, if they used them ill, might take part against them, treated them with kindness. But no sooner were the Tarquins got rid of, and the nobles thus relieved of their fears, when they began to spit forth against the commons all the venom which before they had kept in their breasts, offending and insulting them in every way they could; confirming what I have observed already, that men never behave well unless compelled, and that whenever they are free to act as they please, and are under no restraint everything falls at once into confusion and disorder. Wherefore it has been said that as poverty and hunger are needed to make men industrious, so laws are needed to make them good. When we do well without laws, laws are not needed; but when good customs are absent, laws are at once required.

On the extinction of the Tarquins, therefore, the dread of whom had kept the nobles in check, some new safeguard had to be contrived, which should effect the same result as had been effected by the Tarquins while they lived. Accordingly, after much uproar and confusion, and much danger of violence ensuing between the commons and the nobles, to insure the safety of the former, tribunes were created, and were invested with such station and authority as always afterwards enabled them to stand between the people and the senate, and to resist the insolence of the nobles.