The castle of San Diego stands upon the high bank, and, though commanding the entrance to the harbor, is itself commanded by the surrounding high lands, and has so often been taken by assault during the last thirty years as to be considered untenable. The harbor appears like a nest scooped out of the mountains, into and out of which the tide ebbs and flows through a double channel riven by an earthquake in the solid rock. Tradition says it once had another entrance, but that an earthquake closed it up and opened the present channel. There is still another opening in the sharp mountain ridge that incloses it from the sea, but this opening, dug by the labor of man, at a point opposite the entrance of the harbor, was to let the cool sea-breeze in upon one of the hottest and most unhealthy places upon the continent. Such, in substance, is and was the little city of Acapulco, the seat and focus of the Oriental commerce of New Spain and of all the Spanish empire. WAR OF SANTA ANNA AND ALVAREZ. Santa Anna and Alvarez are the only remaining insurrectionary chiefs in Mexico. When I was last in the capital, Santa Anna was reigning supreme in the vice-royal palace, and Alvarez was supreme at Iztla, the capital of the Department of Guerrero, of which Acapulco is the sea-port town. The two chiefs had been long hostile to each other, but a gold mine, discovered upon the bank of the River Mescala, was "the straw that broke the camel's back." Alvarez had not been consulted in the disposition made of it. Santa Anna felt himself powerful in his newly-equipped army of 23,000 men, the finest army that had ever been seen in Mexico--an army which he was maintaining at a daily cost of $23,000. Alvarez was equally strong in his mountain fastnesses, in the affections of the _Pintos_, or "Spotted People," and, above all, in the poverty of his country. Santa Anna took the initiative by sending 2000 men to garrison Acapulco, and Alvarez committed the first open hostility, by closing the passes against them. Then the campaign began. Santa Anna traveled at the head of his grand army. During his unobstructed march to Acapulco there occurred a great many victories, for victories are indigenous products of Mexico. The siege of the castle of San Diego de Acapulco was the first of the long list of unsuccessful sieges that distinguished the year 1854. The besiegers dared not risk an assault, and they had not sufficient material for conducting a regular siege. For some weeks the opposing forces remained looking at each other, while almost the only blood spilled was by the clouds of musquitoes that hovered over the camp of the grand army, and by the swarms of fleas that infested the castle. It might well be called a bloody war, for few escaped without bearing the scars of wounds and bloodletting.