"But, father," said Phil, "I supposed the Aztecs were the first people in the country!" "So do many people, Phil," was the reply, "but they were not. They were a wandering tribe, as Indians might be, who conquered a people older than themselves called the Nahoas, about whom we know very little. But the Aztecs achieved a good deal of skill in working in stone, and the fact that their monuments are not perishable, makes their civilization enduring in fame." "Then the Nahoas were the first?" queried Roger. But his informant shook his head, smiling slightly. "They may have been," he answered, "but it seems very doubtful. I think we have to go back a great deal further when we start to look for early Americans." "Why?" "Because of the evident age of the remains. For example," he continued, "I don't suppose either of you has been noticing this road?" "I've been wondering at it this last half hour," said Roger. "It isn't like any canyon that I ever saw, and by the way it cuts through different levels of strata it can't have been made by water. And if it's made by hand, why should they cut a road, when it could have been made on the level above with half the trouble?" "You are observant, my boy, and your eye has been well trained," was the approving reply. "But you don't seem to realize that this may be artificial and yet not have been intended for a road, although it is so used now." "Oh, I know," broke in Phil, "it must be a canal." "Hardly big enough for a canal," said his father, "though you are on the right track. This was an irrigating ditch, and if you will notice, at almost regular intervals, smaller dry ditches fork from it. This desert through here is just honeycombed with works of irrigation, great aqueducts, canals and lateral ditches, which at one time must have made this barren waste a field of blossoms." "It seems a shame, somehow," said Roger, "to think of all that work being abandoned." "Abandoned indeed! This place once possibly was the New York or London of its time, but ruins represent all that is left of the cities, and a thousand different kinds of cactus have taken the place of the cornfield and the vineyard. And," he added, pointing ahead, "of all the palaces of those unknown emperors, ruins like these are all that remain." The boys thought it rather a strain on the imagination to picture palaces in the dry square adobe walls, but as they walked up close to them, some lurking hint of former greatness became felt. The Casa Grande must have stood some four or five stories in height and the rooms were rarely less than twenty feet square, so that the idea was given not only of size but also of extreme age, this being due in part, of course, to the softness of the material of which they were built.