Every possible route across the Andes had been examined, and the most careful calculation of distances made. Spies were placed in all the passes, and the Spaniards were kept in absolute ignorance as to which of many passes along hundreds of miles of frontier would be used for the impending attack. These men were sworn to remain “united in sentiment and courage, in order not to suffer for the future any tyrant in America; and like new Spartans never to bear the chains of slavery while the stars shone in the sky and blood ran in their veins.” The precautions of this astute leader are shown by the fact that his real intentions were not revealed until on the very eve of the advance, through fear of treachery. In the middle of January General San Martin broke camp and left Mendoza. His army was divided into two divisions. The smaller force was sent through what is known as the Uspallata pass, which was the old Inca trail, and is now followed by the railway which has just been completed across the Andes. This trail runs across the Bridge of the Incas, one of the most famous natural bridges in the world. The other followed the more difficult pass of Las Platas, farther to the north. The solitude, barrenness and utter desolation of these Andean passes can only be fully appreciated by those who have traversed them as has the writer. Majestic Aconcagua looks down upon both routes, and all around are lofty peaks which seem like giant sentinels guarding these solitudes of nature from the invasion of man. Terrific wind and snow storms are common, and the dust blows in clouds that are almost stifling at times. It was an undertaking that would have appalled an ordinary man. [Illustration: SAN MARTIN AND O’HIGGINS AT LA CUMBRE, CROSSING THE ANDES INTO CHILE Courtesy of the Bulletin of Pan-American Union]