This identity in form of tower and round kiva and the relative abundance of both in the San Juan drainage, leads the author to believe that one was derived from the other, in that district, and spread from it southward and westward until, very much modified, it reached the periphery of the pueblo area. It is believed that, in the earliest time, the isolated tower was constructed for ceremonial purposes and that rooms for habitations were dugouts or other structures architecturally different from it. Later, domiciles were constructed around the base of these towers until they encircled them in a compact mass of rooms. The tower then lost its apparent height, but morphologically retained its form. As this circular type of kiva spread into the pueblo area in course of time it was again constructed independently of the domiciles and the relative numbers diminished until, as in some of the pueblos of the Rio Grande, there survive only one or two kivas for each village, but these are no longer embedded in habitations as in the more advanced archaic conditions. The tower kiva may be regarded as the nucleus of the clan, or the building erected for ceremonies of that clan, the earliest and best constructed stone structures in the region where the pueblo originated. Where there were several clans there were several towers; when one clan, a single tower. In course of time rooms for habitation or possibly for other purposes, clustered about these towers; these units consolidated with rooms and kivas of another type forming a composite pueblo. In this form we find the towers rising above a mass of secular rooms. The archaic form of ceremonial room or tower survived in Cliff Palace and other Mesa Verde ruins.[21] Several circular kivas and towers seen by the author have one or more incised stones, bearing a coiled figure resembling a serpent. One of the best of these has also peripheral lines like conventional symbols of feathers. An obscure legend of the Hopi recounts that the ancestral kivas of the Snake clan, when it lived at Tokonabi, or along the San Juan were circular in form. While at present only a suggestion, it is not improbable that towers and round kivas may have been associated with Snake ceremonials, especially as this cult is known to have survived among Keresan pueblos like Sia and Acoma. The Snake clan of the Hopi according to traditions came from the north or the region of circular kivas.