Thus the slackening of international connections led at once to a distribution of authority between a north and a south Babylonian site. It is true that both capitals were under the same political control, but from the economic standpoint we are forcibly reminded of the era of city-states in Sumer and Akkad. Then, too, there was no external factor to retain the centre of gravity in the north; and Erech more than once secured the hegemony, while the most stable of the shifting dynasties was the latest of the southern city of Ur. The rise of Babylon as the sole and permanent capital of Sumer and Akkad may be traced, as we shall note, to increased relations with Northern Syria, which followed the establishment of her dynasty of West-Semitic kings.[14] And again we may see history repeating herself, when Moslem authority is removed to Baghdad at the close of the first phase in the Arab occupation of Mesopotamia. For on the fall of the Omayyad dynasty and the transference of the Abbasid capital from Damascus to the east, commercial intercourse with Syria and the west was restored to its old footing. Basra and Kûfa at once failed to respond to the changed conditions, and a new administrative centre was required. It is significant that Baghdad should have been built a few miles above Ctesiphon, within the small circle of the older capitals;[15] and that, with the exception of a single short period,[16] she should have remained the capital city of 'Irâk. Thus the history of Mesopotamia under the Caliphate is instructive for the study of the closely parallel conditions which enabled Babylon at a far earlier period to secure the hegemony in Babylonia and afterwards to retain it.