The pottery made by the earliest settlers of South Mesopotamia shows that they came from Persia. At first they retained the tightly interwoven geometric designs used in their homeland;[81] but left to themselves they soon adopted an easier flowing, careless decoration (called Al Ubaid) which remained in use for many centuries and represents the Persian tradition in only a very debased form. In many places it is found on virgin soil, which shows that the settlers spread farther through the country of which they had at first occupied only certain localities. At Ur, for instance, detailed observations were made which reveal the conditions in which men lived when the site was first inhabited. The relevant layers show: a stratum of irregular thickness composed of refuse resulting from human occupation—ashes, disintegrated mud brick, potsherds, etc. This went down almost to sea-level; below it was a belt about one metre thick of mud, grey in colour above, and darkening to black below, much of which was clearly due to the decay of vegetation. In it were potsherds, sporadic above but becoming more numerous lower down and massed thickly at the bottom, all the fragments lying horizontally; they had the appearance of having sunk by their own weight through water into soft mud. At a metre below sea-level came stiff, green clay pierced by sinuous brown stains resulting from the decay of roots; with this all trace of human activity ceased. Evidently this was the bottom of Mesopotamia.[82] Southern Mesopotamia resembled the Egyptian Delta, rather than the Nile valley where cliffs constrain the meanderings of the river, and old banks and spurs provide high ground. In Mesopotamia the lowest course of Euphrates and Tigris presents, even to-day, a wilderness of reed forests where the Marsh Arabs lead an amphibious existence (Fig. 6). All traffic is by narrow bituminous skiffs; the people fish and keep some cattle, living in reed huts built on mattresses of bent and trodden-down reed stems. Their dwellings are described as follows: at one end is a low and narrow aperture which serves as a doorway, window and chimney combined; on the rush-strewn and miry floor sleep men and women, children and buffaloes, in warm proximity ... the ground of the hut often oozing water at every step.[83] The chiefs’ reed tents are more impressive; they are large tunnels of matting covering a framework of reed bundles which form semicircular arches. Doors and windows are arranged in the mats closing either end. We know that such structures were also used in the fourth millennium B.C., for they are represented, with all the necessary detail, in the earliest renderings of sacred buildings, notably the byres and folds of temple animals (Fig. 5).