Both Navajos and Apaches speak dialects of the Athapaskan language which is spoken by many groups in northwestern Canada. At some time in the relatively recent past, groups of Athapaskan-speaking people left their northern homeland and drifted southward, some going along the coast and others wandering farther east. Some reached the Southwest and the descendants of these migrants are the Indians whom we know as Navajos and Apaches. There are many theories as to the route which they followed. Recent finds, in the Colorado Rockies, of circular structures of dry-laid masonry which are non-Pueblo in character and which resemble certain Navajo houses or hogans, suggest that at least some of the migrants may have followed the main mountain ranges.[68] It is also possible that they may have moved south through the Great Basin west of the Rocky Mountains, or along the High Plains east of the mountains. Pottery finds give 1100 A. D. as the earliest date for the hoganlike structures in the Colorado mountains. It is not certain that these houses were built by Athapaskan people, however, and there is no definite knowledge as to just when the Athapaskans reached the Southwest and first came into contact with the Pueblo Indians. The earliest tree-ring date yet obtained in the Pueblo area from any site which we may be sure is Navajo is from the Governador area and falls in the middle of the sixteenth century.[40] If the Navajos arrived as early as 1200 A.D. they may have influenced the Largo-Gallina people and have been influenced by them, but this is still a moot question. A relatively early arrival might also aid in explaining the withdrawal of the Pueblos from the northern area. SUMMARY We may summarize the Great-Pueblo period as follows. It was the period in which the Anasazi culture attained its highest development, and it was marked by intense local specialization. Most of the basic aspects of the culture had already been well established, but there was tremendous improvement and amplification. Unit houses continued to be occupied throughout the period but there was a general coalescence of the population. The trend was toward concentration in great, terraced communal houses, up to five stories in height, and large enough to shelter hundreds of people. Some were built in the open and others in large natural caverns in cliffs. Small kivas, presumably used by small groups such as clans, were incorporated in the houses or placed in the central court. There were also Great Kivas, larger and more elaborate structures, believed to have served an entire community. There was local variation in architectural details, both as regards masonry types and house structures.