It may have been a forced colonization, commanded and carried out by the Chaldaean kings, who may have originated a system of transplanting to distant regions subject tribes of doubtful fidelity; or it may have been the voluntary self-expatriation of an increasing race, pressed for room and discontented with its condition.

Again, it may have taken place by a single great movement, like that of the Tartar tribes, who transferred their allegiance from Russia to China in the reign of the Empress Catherine, and emigrated in a body from the banks of the Dun to the eastern limits of Mongolia or it may have been a gradual and protracted change, covering a long term of years, like most of the migrations whereof we read in history.

On the whole, there is perhaps some reason to believe that a spirit of enterprise about this time possessed the Semitic inhabitants of Lower Mesopotamia, who voluntarily proceeded northwards in the hope of bettering their condition.

Terah conducted one body from Ur to Harran: another removed itself from the shores of the Persian Gulf to those of the Mediterranean; while probably a third, larger than either of these two, ascended the course of the Tigris, occupied Adiabene, with the adjacent regions, and, giving its own tribal name of Asshur to its chief city and territory, became known to its neighbors first as a distinct, and then as an independent and powerful people.
The Assyrians for some time after their change of abode were probably governed by Babylonian rulers, who held their office under the Chaldaean Emperor.

Bricks of a Babylonian character have been found at Kileh-Sherghat, the original Assyrian capital, which are thought to be of greater antiquity than any of the purely Assyrian remains, and which may have been stamped by these provincial governors.