Filing to the left a few yards, the emigrants found a deep fissure through which the animals stumbled one by one over mounds of crumbled adobes. Thurstane, entering last, looked around him in wonder. He was inside a quadrilateral enclosure, apparently four hundred yards in length by two hundred and fifty in breadth, the walls throughout being the same mass of adobe work, fissured, jagged, gray, solemn, and in their utter solitariness sublime. But this was not the whole ruin; the fortress had a citadel. In one corner of the enclosure stood a tower-like structure, forty-five or fifty feet square and thirty in altitude, surmounted on its outer angle by a smaller tower, also four-sided, which rose some twelve or fourteen feet higher. It was not isolated, but built into an angle of the outer rampart, so as to form with it one solid mass of fortification. The material was adobe; but, unlike the other ruins, it was in good condition; some species of roofing had preserved the walls from guttering; not a crevice deformed their gray, blank, dreary faces. Instinctively and without need of command the emigrants had pushed on toward this edifice. It was to be their fortress; in it and around it they must fight for life against the Apaches; here, where a nameless people had perished, they must conquer or perish also. Thurstane posted Kelly and one of the Mexicans on the exterior wall to watch the movements of the savage horde in the plain below. Then he followed the others to the deserted citadel. Two doorways, one on each of the faces which looked into the enclosure, offered ingress. They were similar in size and shape, seven feet and a half in height by four in breadth, and tapering toward the summit like the portals of the temple-builders of Central America. Inside were solid mud floors, strewn with gray dust and showing here and there a gleam of broken pottery, the whole brooded over by obscurity. It was discoverable, however, that the room within was of considerable height and size. There was a hesitation about entering. It seemed as if the ghosts of the nameless people forbade it. This had been the abode of men who perhaps inhabited America before the coming of Columbus. Here possibly the ancestors of Montezuma had stayed their migrations from the mounds of the Ohio to the pyramids of Cholula and Tenochtitlan. Or here had lived the Moquis, or the Zunians, or the Lagunas, before they sought refuge from the red tribes of the north upon the buttes south of the Sierra del Carrizo. Here at all events had once palpitated a civilization which was now a ghost. "This is to be our home for a little while," said Thurstane to Clara. "Will you dismount? I will run in and turn out the snakes, if there are any. Sergeant, keep your men and a few others ready to repel an attack. Now, fellows, off with the packs."