Meanwhile San Martin, behind the screen of the Andes, and only a hundred and fifty miles from Santiago, was forging a thunderbolt destined to shatter into fragments the edifice which Abascal had been so skilfully constructing through seven laborious years. The story of how the silent Argentine gathered and equipped the "Army of the Andes" has already been told. In the chapter devoted to Argentina the reader will find a meagre description of his marvellous march over the cloud-high passes, the descent into the plain of Aconcagua made so suddenly that the Spanish forces could not hurry up to bar his way, the prompt advance over the low transverse range which forms the northern boundary of the plain where Santiago stands, and the overwhelming victory in the gorge of Chacabuco against the pick of the Spanish veterans, who confidently stood to the attack, never dreaming until San Martin was right upon them that his main body had had time to reach the spot. The Spanish authorities at Madrid and Lima had made the irretrievable mistake of underestimating the efficiency of his army. They thought the troops in Chile amply able to take care of any four thousand men the patriots could get together, but San Martin's army was differently provided and organised than the undisciplined masses which had been routed at Huaqui, Villapugio, and Rancagua. The Spanish generals were not so much surprised at his crossing the Andes as at finding the troops which reached the Chilean plains to be well furnished with artillery, cavalry, and ammunition, perfectly ready for an aggressive campaign, and a match man for man for any force that could be brought against them. [Illustration: RAILROAD BRIDGE BETWEEN SANTIAGO AND VALPARAISO.]