Large aggregations of many cells into one cluster are the latest development of pueblo architecture. They were immediately preceded by a type composed of a larger number of smaller villages, located on sites selected with reference to their ease of defense, and apparently the change from the latter to the former type was made at one step, without developing any intermediate forms. The differences between the largest examples of villages on defensive sites and the smallest appear to be only differences of size. Doubtless in the early days of pueblo architecture small settlements were the rule. Probably these settlements were located in the valleys, on sites most convenient for horticulture, each gens occupying its own village. Incursions by neighboring wild tribes, or by hostile neighbors, and constant annoyance and loss at their hands, gradually compelled the removal of these little villages to sites more easily defended, and also forced the aggregation of various related gentes into one group or village. At a still later period the same motive, considerably emphasized perhaps, compelled a further removal to even more difficult sites. The Tusayan villages at the time of the Spanish discovery were located on the foothills of the mesas, and many pueblo villages at that period occupied similar sites. Actuated by fear of the Ute and Comanche, and perhaps of the Spaniards, the inhabitants soon after moved to the top of the mesa, where they now are. Many villages stopped at this stage. Some were in this stage at the time of the discovery--Acoma, for example. Finally, whole villages whose inhabitants spoke the same language combined to form one larger village, which, depending now on size and numbers for defense, was again located on a site convenient for horticulture.