You catch the first glimpse of the ruins about eighteen miles out--a red roof put on by the Government, then a huge, square, four story mass of ruins surrounded by broken walls, with remnants of big elevated courtyards, and four or five other compounds the size of this central house, like the bastions at the four corners of a large, old-fashioned walled fort. The walls are adobe of tremendous thickness--six feet in the house or temple part, from one to three in the stockade--a thickness that in an age of only stone weapons must have been impenetrable. The doors are so very low as to compel a person of ordinary height to bend almost double to enter; and the supposition is this was to prevent the entrance of an enemy and give the doorkeeper a chance to eject unwelcome visitors. Once inside, the ceilings are high, timbered with _vigas_ of cedar strengthened by heavier logs that must have been carried in a horseless age a hundred miles from the mountains. The house is laid out on rectangular lines, and the halls straight enough but so narrow as to compel passage sidewise. In every room is a feature that has puzzled scientists both here and in the cave dwellings. Doors were, of course, open squares off the halls or other rooms; but in addition to these openings, you will find close to the floor of each room, little round "cat holes," one or two or three of them, big enough for a beam but without a beam. In the cave dwellings these little round holes through walls four or five feet thick are frequently on the side of the room opposite the fireplace. Fewkes and others think they may have been ventilator shafts to keep the smoke from blowing back in the room, but in Casa Grande they are in rooms where there is no fireplace. Others think they were whispering tubes, for use in time of war or religious ceremony; but in a house of open doors, would it not have been as simple to call through the opening? Yet another explanation is that they were for drainage purpose, the cave man's first rude attempt at modern plumbing; but that explanation falls down, too; for these openings don't drain in any regular direction. Such a structure as Casa Grande must have housed a whole tribe in time of religious festival or war; so you come back to the explanation of ventilator shafts.