The two beams at the rear of the room above have been in place for 800 years. Tree-ring dates obtained from various beams in the pueblo span from 1106 to 1220 but cluster around three periods: 1137, 1160, and 1190. This suggests specific periods of construction, or at least beam cutting. Many room walls also abut one another-evidence that a room was added on to one already in place. Perhaps the various building phases mark the arrival of clans, each bringing something different to the community, resulting in the "cultural brew" that makes Wupatki so unusual. Some archeologists see cultural traditions, such as Sinagua and Kayenta, not as "people" or genetic and ethnic groups, but rather as inhabited geographic regions experiencing a dynamic ebb-and-flow of populations. Migrations brought people together creating cultural dominance in some areas and shared cultural traits in others. Seen this way, specific traditions such as black-on-white pottery and T-shaped doorways could have been maintained over centuries by peoples of different linguistic and ethnic backgrounds.