The immediate successors of Tukulti-Ninib I appear to have been perpetually engaged in war with the Babylonians, who at no period of their history readily submitted to the Assyrian yoke. Tiglath-Pileser I’s accession to the throne about 1100 B.C. inaugurated a new period in the history of Assyrian expansion. Some of the mountain-tribes who had owed allegiance to former Assyrian monarchs had revolted, and Tiglath-Pileser made it his business to crush them. The northern Moschians who sixty years previously had been the vassals of Assyria, had under the leadership of five kings invaded the territory of Commagene, but they were effectively reduced by Tiglath-Pileser, and the land of Commagene was conquered “throughout its whole extent.” Various other tribes in the north, of whom the Nairi would appear to have been the most important, were similarly brought beneath the Assyrian sway. In a campaign against Babylonia he was also successful for the moment, and effected the reduction of Babylon, Sippar, Opis and other cities in Lower Mesopotamia. But his triumph here was short-lived, and the Assyrians were expelled by Marduk-nadin-akhê, the king of Babylon, who further invaded Assyria, and carried off the statues of some of the Assyrian gods. Ashur-bêl-kala, the son and successor of Tiglath-Pileser I, retrieved the fortunes of the Assyrian arms in the south, and forced Marduk-shapik-zêrim the successor of Marduk-nadin-akhê to sue for peace. But after the reigns of Tiglath-Pileser I’s two sons, Assyria suffered a severe disaster at the hands of the Hittites, and lost the territory gained by Tiglath-Pileser. Northern Syria which had been compelled to acknowledge the suzerainty of Tiglath-Pileser, now asserted her independence, and for some time remained the mistress of her own destinies. Thus Assyria for the time being lost her position as a world-power, and it was only in the reign of Tukulti-Ninib II (890-885 B.C.) that her fortunes began to revive. The Nairi were again reduced by this king, and apparently the whole of the valley of the Upper Tigris was once more subjugated. Ashur-naṣir-pal (885-860 B.C.) carried on the work of expansion and re-conquest. With the further extension of Assyrian power northwards, the need of a capital occupying a more central position than ancient Ashur was at once realized, and accordingly Ashur-naṣir-pal transferred the seat of his government to Calah (Nimrûd) some forty miles north of Ashur. Nearly 500 years before, Shalmaneser I had laid the foundations of a town at Calah, but the unsettled circumstances of the time had retarded its growth. Ashur-naṣir-pal demolished what remained of the old town, and founded a new town on the same site, and for at least a century Calah remained the capital of the empire.