An Assyrian conquest of the country is here represented, amid all the difficulties presented by its swamps and reed-beds. (After a bas-relief at Nineveh.)] It is clear that the pressure exerted upon Babylonia by the West-Semitic migration must have tended to displace sections of the existing population. The direction of advance was always down-stream, and the pressure continued in force even after the occupation of the country. Those strains in the population, which differed most radically from the invaders, would be the more likely to seek sanctuary elsewhere, and, with the exception of Elam, the Sea-Country offered the only possible line of retreat. We may assume, therefore, that the marsh-dwellers of the south had been reinforced for a considerable period by Sumerian refugees, and, though the first three rulers of the new kingdom bore Semitic names and were probably Semites, the names of later rulers of the Sea-Country suggest that the Sumerian element in the population afterwards secured the control,[7] no doubt with the assistance of fresh drafts from their own kindred after their successful occupation of Southern Babylonia. Under the more powerful kings of the Second Dynasty, the kingdom may have assumed a character resembling that of its predecessors in Babylonia. The centre of administration was certainly shifted for a time to Nippur, and possibly even further north, but the Sea-Country, as the home-land of the dynasty, must have always been regarded as a dominant province of the kingdom, and it offered a secure refuge to its rulers in the event of their being driven again within its borders. In spite of its extensive marshes, it was capable of sustaining its inhabitants in a considerable degree of comfort, for the date-palm flourished luxuriantly, and the areas under cultivation must have been at least as productive as those further to the north-west. Moreover, the zebu, or humped cattle of Sumer, thrived in the swamps and water-meadows, and not only formed an important source of supply, but were used for ploughing in the agricultural districts.[8] With such a country as a base of operations, protected in no small degree by its marshes, it is not surprising that the Sea-Country kings should have met with considerable success in their efforts at extending the area of territory under their control.