The mitigation of the lot of the slave constitutes so important a phase of the moral evolution of the pre-Christian period that we must consider it here apart and in some detail. The causes of this moral reform were various. Among the most efficient agencies were Stoicism and the other Greek philosophies.[574] Then the character of many of the slaves themselves, the equal or superior often of their master in intelligence and culture, won for the class respect and consideration. Furthermore, the great number of freedmen, who constituted a very large element of the free population of the Empire,[575] tended to create a public sentiment favorable to the slave. Having had, like Epictetus the Stoic, acquaintance with the bitterness of bondage, they knew how to pity the bondsman. Already in the first century of the Empire all the chief leaders of moral reform taught that the slave is the equal of his master in capacity for virtue.[576] Dion Chrysostom condemned hereditary slavery as contrary to the Law of Nature and hence wrong. He is thought to have been the earliest writer in the Roman Empire to take this advanced moral ground.[577] Seneca proclaimed the obligations of the higher law: “Although our laws,” he says, “permit a master to treat his slave with every degree of cruelty, still there are some things that the common law of life forbids being done to a human being.”[578] Cruel masters, he adds, are hated and detested. The growing sentiment of tenderness for the slave found significant popular expression in the reign of Nero. A certain prefect of the city having been murdered by a slave, the Senate, in accordance with ancient usage, adjudged to death the entire household of slaves, four hundred in number. Sentiment in the Senate itself was divided, some of the senators voting against the proposal, while the people gathering in seditious crowds threatened to prevent by force the carrying out of the edict. A body of soldiers was necessary to overawe the populace and secure the execution of the slaves.[579] A little later we see these growing humanitarian feelings reflected in the imperial legislation. Hadrian took away from masters the ancient right willfully to kill their slaves; and Antoninus Pius made the killing of a slave, _sine causa_, murder. The edicts of other emperors effected further mitigations of the law, so that the slave code of the later pagan Empire is characterized by a humaneness of spirit that places it in strong contrast with the callousness of the code of earlier times. Additional evidence of the increased humanity of the age is afforded by the numerous manumissions of slaves.[580] The motives that prompted such action were undoubtedly mixed, one self-regarding motive being the ambition to have a great retinue of clients;[581] but the dominant motive is unquestionably to be sought in the growing humanity of the age.