In many cases they refused the boon of liberty and defied the most horrible tortures rather than betray their masters, accompanied them in their flight when all others had abandoned them, displayed undaunted courage and untiring ingenuity in rescuing them from danger, and in some cases saved the lives of their owners by the deliberate sacrifice of their own.(580) This was, indeed, for some time the pre-eminent virtue of Rome, and it proves conclusively that the masters were not so tyrannical, and that the slaves were not so degraded, as is sometimes alleged. The duty of humanity to slaves had been at all times one of those which the philosophers had most ardently inculcated. Plato and Aristotle, Zeno and Epicurus, were, on this point, substantially agreed.(581) The Roman Stoics gave the duty a similar prominence in their teaching, and Seneca especially has filled pages with exhortations to masters to remember that the accident of position in no degree affects the real dignity of men, that the slave may be free by virtue while the master may be a slave by vice, and that it is the duty of a good man to abstain not only from all cruelty, but even from all feeling of contempt towards his slaves.(582) But these exhortations, in which some have imagined that they have discovered the influence of Christianity, were, in fact, simply an echo of the teaching of ancient Greece, and especially of Zeno, the founder of Stoicism, who had laid down, long before the dawn of Christianity, the broad principles that ’all men are by nature equal, and that virtue alone establishes a difference between them.’(583) The softening influence of the peace of the Antonines assisted this movement of humanity, and the slaves derived a certain incidental benefit from one of the worst features of the despotism of the Cæsars. The emperors, who continually apprehended plots against their lives or power, encouraged numerous spies around the more important of their subjects, and the facility with which slaves could discover the proceedings of their masters inclined the Government in their favour.