His _Topica_, or treatise on commonplaces, has less extent and variety of plan, being little else than a compendium of Aristotle's work on the same subject. It was, as he informs us in its proem, drawn up from memory on his voyage from Italy to Greece, soon after Caesar's murder, and in compliance with the wishes of Trebatius, who had some time before urged him to undertake the translation.[208] Cicero seems to have intended his _De Oratore_, _De claris Oratoribus_, and _Orator_, to form one complete system.[209] Of these three noble works the first lays down the principles and rules of the rhetorical art; the second exemplifies them in the most eminent speakers of Greece and Rome; and the third shadows out the features of that perfect orator, whose superhuman excellences should be the aim of our ambition. The _De Oratore_ was written when the author was fifty-two, two years after his return from exile; and is a dialogue between some of the most illustrious Romans of the preceding age on the subject of oratory. The principal speakers are the orators Crassus and Antonius, who are represented unfolding the principles of their art to Sulpicius and Cotta, young men just rising in the legal profession. In the first book, the conversation turns on the subject-matter of rhetoric, and the qualifications requisite for the perfect orator. Here Crassus maintains the necessity of his being acquainted with the whole circle of the arts, while Antonius confines eloquence to the province of speaking well. The dispute for the most part seems verbal; for Cicero himself, though he here sides with Crassus, yet elsewhere, as we have above noticed, pronounces eloquence, strictly speaking, to consist in beauty of diction. Scaevola, the celebrated lawyer, takes part in this preliminary discussion; but, in the ensuing meetings, makes way for Catulus and Caesar, the subject leading to such technical disquisitions as were hardly suitable to the dignity of the aged Augur.[210] The next morning Antonius enters upon the subject of invention, which Caesar completes by subjoining some remarks on the use of humour in oratory; and Antonius, relieving him, finishes the morning discussion with treating of arrangement and memory. In the afternoon the rules for propriety and elegance of diction are explained by Crassus, who was celebrated in this department of the art; and the work concludes with his handling the subject of delivery and action. Such is the plan of the _De Oratore_, the most finished perhaps of Cicero's compositions. An air of grandeur and magnificence reigns throughout. The characters of the aged senators are finely conceived, and the whole company is invested with an almost religious majesty, from the allusions interspersed to the melancholy destinies for which its members were reserved.