It will have been noted that all the Sumerian mounds described or referred to in the preceding paragraphs cover cities which, after being burned down and destroyed in a comparatively early period, were never reoccupied, but were left deserted. Lagash, Umma, Shuruppak, Kisurra, and Adab play no part in the subsequent history of Babylonia. We may infer that they perished during the fierce struggle which took place between the Babylonian kings of the First Dynasty and the Elamite kings of Larsa. At this time city after city in Sumer was captured and retaken many times, and on Samsu-iluna's final victory over Rîm-Sin, it is probable that he decided to destroy many of the cities and make the region a desert, so as to put an end to trouble for the future. As a matter of fact, he only succeeded in shifting the area of disturbance southwards, for the Sumerian inhabitants fled to the Sea-country on the shores of the Persian Gulf; and to their influence, and to the reinforcements they brought with them, may be traced the troubles of Samsu-iluna and his son at the hands of Iluma-ilu, who had already established his independence in this region. Thus Samsu-iluna's policy of repression was scarcely a success; but the archaeologist has reason to be grateful to it. The undisturbed condition of these early cities renders their excavation a comparatively simple matter, and lends a certainty to conclusions drawn from a study of their remains, which is necessarily lacking in the case of more complicated sites. Another class of Sumerian cities consists of those which were not finally destroyed by the Western Semites, but continued to be important centres of political and social life during the later periods of Babylonian history. Niffer, Warka, Senkera, Mukayyar, and Abû Shahrain all doubtless contain in their lower strata remains of the early Sumerian cities which stood upon their sites; but the greater part of the mounds are made up of ruins dating from a period not earlier than that of the great builders of the Dynasty of Ur. In Nippur, during the American excavations on this site, the history of Ekur, the temple of the god Enlil, was traced back to the period of Shar-Gani-Sharri and Narâm-Sin;[24] and fragments of early vases found scattered in the _débris_ beneath the chambers on the south-east side of the Ziggurat, have thrown valuable light upon an early period of Sumerian history. But the excavation of the pre-Sargonic strata, so far as it has yet been carried, has given negative rather than positive results. The excavations carried out on the other sites referred to were of a purely tentative character, and, although they were made in the early fifties of last century, they still remain the principal source of our knowledge concerning them. [Illustration: WARKA after Loftus]