Then another company of people looking for a permanent dwelling place would chance upon this hill. Finding it suited to their requirements they would immediately start building upon the surface. With no knowledge whatever that a previous group of people had made this hill their habitation, the new dwellings and walls would rise high upon the covered ruins of the earlier period. Within a comparatively short time they also would be the victims of some wandering conqueror, and once again the wrecked habitations of men would be repossessed by the drifting sands of the desert. It is not uncommon that in the course of a thousand years such an experience would be repeated from three or four to a dozen times upon the same site. When the archeologist finds such a mound or hill, he has a treasure indeed. By excavating this deposit one stratum at a time, he builds up a stratographical record which is highly important in reconstructing a consecutive history of this region. The date factors of the various strata are generally established by the contents of each horizon of dwelling, in turn. If the archeologist depends upon facts instead of his imagination, a credible chronology for the entire region can thus be constructed. In such a recovery the common life of the people of antiquity is revealed in amazing detail. We learn their customs of living, something of their arts and crafts and their manner of labor. Their knowledge of architecture is clearly portrayed through such ruins as remain, and the general picture of the incidental events that made up their living is clearly developed as the work proceeds. Since the destruction of such a city was usually catastrophic, the record suddenly breaks off at the point of the tragedy. The abruptness wherewith the life and activity ceased, leaves all of the valuable material undisturbed _in situ_. This circumstance, though unfortunate for the ancients, is a happy one for the archeologist who thus is enabled to rebuild their times and lives. These sites yield many types of material. In establishing chronology, the most important of all of these is probably the pottery. There is no age of men so ancient that it does not yield proof of human ability in the ceramic art. Without aluminum cooking utensils or iron skillets, the folk of antiquity depended upon clay for the vessels of their habitation. Dishes, pots, jars, and utensils of a thousand usages were all made of this common substance. Before the invention of paper, clay was also the common material for preserving written records. As each race of people had its own peculiarities in the use of clay, the pottery that is found on a given site is one of the finest indications of a date factor that the site can contain.