Another very remarkable feature of later Stoicism was its increasingly introspective character. In the philosophy of Cato and Cicero, virtue was displayed almost exclusively in action. In the later Stoics, self-examination and purity of thought were continually inculcated. There are some writers who, with an obstinacy which it is more easy to explain than to excuse, persist, in defiance of the very clearest evidence to the contrary, in representing these virtues as exclusively Christian, and in maintaining, without a shadow of proof, that the place they undeniably occupy in the later Roman moralists was due to the direct or indirect influence of the new faith. The plain fact is that they were fully known to the Greeks, and both Plato and Zeno even exhorted men to study their dreams, on the ground that these often reveal the latent tendencies of the disposition.(395) Pythagoras urged his disciples daily to examine themselves when they retired to rest,(396) and this practice soon became a recognised part of the Pythagorean discipline.(397) It was introduced into Rome with the school before the close of the Republic. It was known in the time of Cicero(398) and Horace.(399) Sextius, one of the masters of Seneca, a philosopher of the school of Pythagoras, who flourished chiefly before the Christian era, was accustomed daily to devote a portion of time to self-examination; and Seneca, who at first inclined much to the tenets of Pythagoras,(400) expressly tells us that it was from Sextius he learnt the practice.(401) The increasing prominence of the Pythagorean philosophy which accompanied the invasion of Oriental creeds, the natural tendency of the empire, by closing the avenues of political life, to divert the attention from action to emotion, and also the increased latitude allowed to the play of the sympathies or affections by the later Stoics, brought this emotional part of virtue into great prominence. The letters of Seneca are a kind of moral medicine applied for the most part to the cure of different infirmities of character. Plutarch, in a beautiful treatise on “The Signs of Moral Progress,” treated the culture of the feelings with delicate skill. The duty of serving the Divinity with a pure mind rather than by formal rites became a commonplace of literature, and self-examination one of the most recognised of duties. Epictetus urged men so to purify their imaginations, that at the sight of a beautiful woman they should not even mentally exclaim, “Happy her husband!”(402) The meditations of Marcus Aurelius, above all, are throughout an exercise of self-examination, and the duty of watching over the thoughts is continually inculcated.