Architectural morphology is the study of how shifting cultural and environmental conditions produce changes in an architectural form. When applied to the mission churches of New Mexico exemplifying seventeenth- and eighteenth-century Spanish colonial architecture in what is now the southwestern United States, architectural morphology reveals much about how Native American culture transformed the traditional European church architecture of the Spanish missionaries who hoped to convert Native Americans to Christianity. Many studies of these mission churches have carefully documented the history and design of their unique architectural form, most attribute the churches' radical departure from their sixteenth-century European predecessors to local climate and a less-mechanized building technology. Certainly, the limitations imposed by manual labor and the locally available materials of mud-brick and timber necessitated a divergence from the original European church model. However, the emergence of a church form suited to life in the Southwest was rooted in something more fundamental than material and technique. The new architecture resulted from cultural forces in both the Spanish colonial and indigenous Native American societies, each with competing ideas about form and space and different ways of conveying these ideas symbolically. For example, the mission churches share certain spatial qualities with the indigenous kiva, around, partly subterranean room used by many Southwest Native American communities for important rituals. Like the kiva it was intended to replace, the typical mission church had thick walls of adobe (sun-dried earth and straw), a beaten-earth floor, and one or two small windows. In deference to European custom, the ceilings of these churches were higher than those of the traditional kiva. However, with the limited lighting afforded by their few small windows, these churches still suggest the kiva's characteristically low, boxlike, earth-hugging interior. Thus, although pragmatic factors of construction may have contributed to the shape of the mission churches, as earlier studies suggest, the provision of a sacred space consistent with indigenous traditions may also have been an important consideration in their design. The continued viability of the kiva itself in Spanish mission settlements has also been underestimated by historians. Freestanding kivas discovered in the ruins of European-style missionary communities have been explained by some historians as examples of "superposition". Under this theory, Christian domination over indigenous faiths is dramatized by surrounding the kiva with Christian buildings. However, as James Ivey points out, such superposition was unlikely, since historical records indicate that most Spanish missionaries, arriving in the Southwest with little or no military support, wisely adopted a somewhat conciliatory attitude toward the use of the kiva at least initially. This fact, and the careful, solitary placement of the kiva in the center of the mission-complex courtyards, suggests an intention to highlight the importance of the kiva rather than to diminish it.