his dwellings. Another powerful influence created architectural modifications in these two regions. In the mountains the village builders were beset on all sides by hostiles or nomads bent on plunder. It was here necessary for man to construct his building with a view to defense by concentration of the rooms. The level plains of southern Arizona and the rivers with a constant flow of water brought about irrigation along the Gila, thus making possible a larger population. All these conditions, reflected in the character of the buildings in the southern region, as contrasted with the northern, have greatly modified the culture and sociological conditions of the aborigines of the two localities. In their extension their boundaries met each other and their contact has led to types of buildings with characters of both. In one locality, Hopi, the circular kiva has disappeared, and a rectangular room has taken its place. Both Hopi and Zuñi pueblos have descendants of the ancestral clans from the Gila still surviving, and there we find the pueblo type with rectangular kivas both enclosed in house masses and separated from them. Offshoots of the mountain or pueblo culture following down the San Juan River penetrated to Hopi and settled at Walpi, shortly after which they were joined by clans from Little Colorado bringing Gila culture, as is recounted in legends still existing. The mountain culture introduced the terraced form of building and the kiva free from the house masses. But this kiva has a rectangular form due either to the configuration of the mesa top or to influences from the south, where the sacred room is rectangular and enclosed by dwellings. In a case of Zuñi we have the plain type or southern contingent predominating, the original settlement at Zuñi having been made by clans from the far south, which were later joined and modified by those from the north. Here we have at the present day the sacred room of rectangular shape hidden away among the dwellings. This was a secondary condition probably brought about by the influence of Catholic missionaries, who forced the Zuñi to abandon their sacred room in the courts of the town, and resort to secrecy to perform the forbidden rites. Both Hopi and Zuñi show in their architecture the influence of two component stocks or peoples, a fact more strikingly brought out in their religious ceremonials. The prehistoric center of pueblo culture origin is situated many miles distant from the area now inhabited by its survivals. When the Spanish travelers first came in touch with this unique condition of life, its center of origin was no longer inhabited. Legendary accounts still survive in the modern pueblos that they came from the north; our main source of information or proof of the truth of these legends is the character of architecture and pottery obtained from the northern ruins, aided by what may be gathered from the modified architecture of the inhabited pueblos, or from historical documents.