Consider another line of development. The buildings we have already considered were erected primarily for the preservation and protection of material possessions. Man, in whatever stage, regards it as necessary to construct a building for religious purposes; in many instances this structure is nothing more than a row of upright stones enclosing an area devoted to his gods. No roof was considered necessary since the objects of worship were practically forces of nature. As time went on, priests or congregations gathered to perform rites within the circular or other areas, or in their neighborhood. These ceremonies rendered secrecy necessary. A priesthood developed with a systematic ritual, which had to be hidden from the eyes of the inquisitive by roofs and side walls, thus forming a building, from which developed the temple or sacred room. Subsequently other buildings were annexed for habitations of priests or laymen. A condition of this kind occurs in our prehistoric Southwestern architecture. The sanctuary in this region is a well-constructed circular building, of peculiar type. It was not a dwelling but a place of ceremonious worship. Habitations distinct from these ceremonial rooms had walls so perishable that traces of them are hard to find, the sanctuary walls alone remaining as an indication of the building art of that period. A more advanced stage along this line of evolution was the addition of rooms with permanent walls to the base of the sanctuary, by which a union of two different kinds of buildings, sacred and secular, was brought about. These three lines of architectural development in our prehistoric Southwest verged in a parallel development into the same form, all starting from the rudest structure and culminating in an almost identical type, one the cave habitation, the other the storage room with its annex, and the third the sacred building or sanctuary, around which are clustered rooms for secular purposes. A combination of the three types, producing a composite cluster, gives us what is called the terraced community house or pueblo. The term “pueblo,” signifying a village or town, was applied by Spanish explorers to Indian villages in our Southwest at the close of the sixteenth century. Certain other collections of houses, to which the word “rancherias” (ranches) was applied, were also mentioned, the distinction between the two being that the buildings of the latter were more widely scattered. At present we speak of pueblo and pueblo culture in a more exact way, and in a scientific discussion of the origin of this culture it is necessary to restrict the Spanish terms, or to define a pueblo from a cultural point of view. This leads to an enumeration of distinctive architectural features which characterize the two types.