The taciturn general in Cuyo was, however, preparing a thunderbolt that would clear the Argentine sky of all these clouds except that most portentous of all--civil war. After three years of incessant preparation, San Martin believed that his army was ready to undertake the great campaign. Though it numbered only four thousand men, it was the most efficient body of troops that ever gathered on South American soil. Among the Argentine contingent were the picked youth of Buenos Aires and the provinces--reckless, enthusiastic youths whose ambition, patriotism, or love of adventure made them willing to follow anywhere San Martin might dare to lead. Not inferior to their white comrades were the manumitted negroes. The cruelest charges and the heaviest losses fell to their lot and few of them ever returned over the Andes. The Chilean exiles were picked men--those who preferred death to submission, or who had offended so deeply that their only hope of seeing their homes was to return sword in hand. This force had been drilled and instructed in all the art of war as practised during the Napoleonic era by San Martin himself, a veteran soldier of the great European campaigns--one who had fought with Wellington and against Massena and Soult. He was indefatigable in attending to details, and he seems to have foreseen everything. The last months were spent in preparing rations of parched corn and dried beef; in gathering mules for mountain transportation, and in making sledges to be used on the slopes which were too steep for cannon on wheels. The most careful calculations were made of the distances to be traversed; every route was surveyed; spies were in every pass; the Spaniards were kept in uncertainty as to which of the numerous passes along hundreds of miles of frontier would be used for the attack. San Martin's real intentions were not revealed by him even to the members of his staff until the very eve of the advance.