But the custom, in so far as it concerned Christian prisoners, was condemned by the Christian conscience as incompatible with the spirit of Christianity, and the rule was established that such captives should not be enslaved.[689] We observe the first clear workings of this new war conscience in Britain after the conversion of the Saxon invaders. The Celts of Britain were Christians, and the Saxons, after they themselves had been won over to Christianity, ceased to sell into slavery their Celtic captives. Gradually this new rule was adopted by all Christian nations. No other advance of equal importance marks the moral history of public war during the medieval period. This humane rule, however, did not, as we have intimated, embrace non-Christians. Our word “slave” bears witness to this fact. This term came to designate a person in servitude from the circumstance that up to the eleventh century, which saw the evangelization of Russia, the slave class in Europe was made up largely of _Slavs_, who, as pagans, were without scruple reduced to slavery by their Christian captors. But the earlier rights which the immemorial laws of war conferred upon the captor were not wholly annulled in the case of Christian captives. The practice of holding for ransom took the place of sale into slavery. This custom prevailed throughout the feudal period, but gradually during the seventeenth and eighteenth centuries this practice finally yielded to the more humanitarian custom of exchange of prisoners.[690] Thus in this department of ethics there is to be traced a gradual humanization of the code, which, beginning in savagery with gross cannibalism and torture, advances through killing in cold blood, sale into slavery, and holding for ransom, to equal exchange. [Sidenote: Morality in the monasteries: moral significance of the rise of the Mendicant Orders] During the age of chivalry the ideal of the knight overshadowed the ideal of the monk. Nevertheless throughout the whole period the monastic ideal inspired a great deal of moral enthusiasm. The founding and endowment of monasteries divided with the equipping of knightly expeditions for the Crusades the zeal and efforts and sacrifices of the European peoples. In the old orders of monks, however, zeal for the ascetic ideal would often grow cold, and the high moral standard of the earlier time would be lowered. Then some select soul, set aflame by a fresh vision of the ideal, would draw together a group of devoted followers, and thus would come into existence a new order of monks, among whom the flame of a holy enthusiasm would burn brightly for a time.[691] Among the numerous new orders called into existence by these reform movements there were two which, in the ideal of duty which they followed, stand quite apart from the ordinary monastic orders. This new ideal had its incarnation in St. Francis[692] and St. Dominic, the founders respectively of the Franciscan and the Dominican order of friars.