The Spaniards, giving little attention to ruins in the country through which their route lay, confined the term “pueblo” to inhabited towns. These early travelers found the majority of these in a limited area along the Rio Grande or along the Little Colorado and in the mountains of what is now northern Arizona. There were wide expanses of country not visited by the Spaniards, which we now know had at that time ruined buildings indicative of a past population, that are similar in form to those inhabited. We find on scientific examination evidence that the life in them was higher in development than in the villages seen by the explorers. Manifestly our subject must be so treated that all pueblos, whether uninhabited or inhabited, should be taken into account in morphological studies. On comparison of ruined pueblos with those inhabited in the sixteenth century certain identities in form are revealed, but there are found also radical differences showing degrees of culture. Indications exist that certain arts of the later pueblos have degenerated: the masonry is not so good and pottery, textiles, and other manufactured articles are inferior. The accounts given by early Spanish chroniclers afford scanty information on details of arts, and historical documents are correspondingly imperfect. In consideration of the subject from the point of view of chronology, our knowledge must be derived, not from previous histories but from archeological remains that are fortunately very abundant through the whole region. The simplest type of pueblo building, called the unit type, consists of one or more rectangular rooms and a circular chamber. This form passes imperceptibly into the linear type, a row of single rooms united by the side of one circular room midway in length. The linear type naturally may have single or multiple rooms, or it may be composed of one or more rows parallel with each other, the doorways opening on the same side or in the same direction. When the lines of rooms are double, and the doorways of each row open in opposite directions, we may designate this the double linear having external doorways. Linear ruins may be one or more stories high; when there is more than one story, doors or lateral openings are generally wanting. On the ground floor, which is entered from the roof, the superimposed rooms have lateral passageways from the roof of the lower story. A double row of buildings may be set in such a way that the doorways face each other, or four such rows may form a rectangle enclosing a court, which often lacks one side. Another type has the pyramidal form, made up of rooms crowded together with the superimposed stories opening in all directions. Wholly different in form from the various linear types above enumerated are the circular buildings enclosing a central court on which the doorways of the lowest story open, and which those of the upper stories face.