Cicero speculated after a mode which admitted of great freedom to his genius, controlled by no particular sect, but was at heart most interested in the severest principles, and became almost a Stoic. Doubtless that was the noblest school then extant, the most harmonious with the spirit of Rome, and which preserved her greatest citizens amid the dissoluteness and ferocity of her imperial career. The ennobling influence exerted by that system was exemplified while it exalted the slave of one of Nero's courtiers to become an efficient moral teacher, and breathed equity and mercy into the ordinary concerns of every man. Especially was it honored by the examples of Marcius Portius Cato, and of Marcus Aurelius Antoninus, who did much to keep alive a loftier regard for virtue and truth throughout all time. The historians of philosophy have often admired the memorable scenes in which Cæsar mastered a nobility of which Lucullus and Hortensius, Sulpicius and Catullus, Pompey and Cicero, Brutus and Cato, were members. From the time of Scipio, they had sought the Greek philosophy as an amusement or an ornament. The influence of the degenerate Grecian systems was exerted upon all the leading spirits of Rome during five centuries, from Carneades to Constantine. Cassius was an Epicurean, and so was the adroit time-server Atticus, the courtier of each fortunate tyrant of the hour, who could embrace Cicero in all the apparent frankness of true friendship, and then abandon him to kiss the hand of Anthony, imbrued in his blood. Marcus Brutus represented the nobler school of Plato; and if in a fearful crisis he trampled on all venerable precedents of justice to guard the sacred principle itself, it was the result of a direful necessity which he could neither avoid nor resist.