But so far as his letter to the monarchs went, Columbus knew, even while writing it, that real gold and the promise of gold were two very different things. His promises could never fill up the empty hold of the ship that was going back to Spain; and so, failing the rich cargo which the men of La Navidad were to have gathered, Columbus bethought himself of some other way in which his discoveries might bring money to the Spanish Crown. The plan he hit upon was the plan of a sick, disappointed, desperate man, as will be seen from a portion of his letter. The letter, intended for the sovereigns, was addressed, as was the custom, to their secretary. "Considering what need we have for cattle and beasts of burden ... their Highnesses might authorize a suitable number of caravels to come here every year to bring over said cattle and provisions. These cattle might be paid for with _slaves_ taken from among the Caribbeans, who are a wild people fit for any work, well built and very intelligent; and who, when they have got rid of the cruel habits to which they have been accustomed, will be better than any other kind of slaves." Horrible, all this, we say, but it was the fifteenth century. Slavery had existed for ages, and many still believed in it, for men like the good Las Casas were few. Moreover, Columbus was tormented by a feeling of not having "made good." He had promised his sovereigns all sorts of wealth, and instead he had been able to collect only an insignificant amount of gold trinkets on Haiti. Desperate for some other source of wealth, in an evil moment he advised slave-catching. Besides considering himself to have fallen short in the royal eyes, he was hounded by the complaints and taunts of the men who had accompanied him. They hated work, so he tried to appease them by giving them authority to enslave the natives; and, as our good Las Casas wisely remarks, "Since men never fall into a single error ... without a greater one by and by following," so it fell out that the Spaniards were cruel masters and the natives revolted; to subdue them harsher and harsher measures were used; not till most of them had been killed did the remaining ones yield submissively. CHAPTER XV ON A SEA OF TROUBLES