This treatise Cicero evidently considered, and not without reason, as his master-work. It was written in the prime of his mental vigor, in the fifty-fourth year of his age, after ample experience in the affairs of State, and while he still hoped, more than he feared for the future of Rome. His object was to discuss in detail the principles and forms of civil government, to define the grounds of preference for a republic like that of Rome in its best days, and to describe the duties and responsibilities of a good citizen, whether in public office or in private life. He regarded this treatise, in its ethics, as his own directory in the government of his province of Cilicia, and as binding him, by the law of self-consistency, to unswerving uprightness and faithfulness, He refers to these six books on the Republic as so many hostages [Footnote: _Praedibus_.] for his uncorrupt integrity and untarnished honor, and makes them his apology to Atticus for declining to urge an extortionate demand on the city of Salamis. The work is in the form of Dialogues, in which, with several interlocutors beside, the younger Africanus and Laelius are the chief speakers; and it is characterized by the same traits of dramatic genius to which I have referred in connection with the _De Amicitia_. The _De Republica_ was probably under interdict during the reigns of the Augustan dynasty; men did not dare to copy it, or to have it known that they possessed it; and when it might have safely reappeared, the republic had faded even from regretful memory, and there was no desire to perpetuate a work devoted to its service and honor. Thus the world had lost the very one of all Cicero's writings for which he most craved immortality. The portions of it which Mai has brought to light fully confirm Cicero's own estimate of its value, and feed the earnest--it is to be feared the vain--desire for the recovery of the entire work. Scipio's Dream, which, is nearly all that remains of the Sixth Book of the _De Republica_, had survived during the interval for which the rest of the treatise was lost to the world. Macrobius, a grammarian of the fifth century, made it the text of a commentary of little present interest or value, but much prized and read in the Middle Ages. The Dream, independently of the commentary, has in more recent times passed through unnumbered editions, sometimes by itself, sometimes with Cicero's ethical writings, sometimes with the other fragments of the _De Republica_.