The Babylonian Empire likewise degenerated under the Cossæan kings, and gave way to the ascendancy of Assyria, which came to regard Babylon with deadly hatred. The capitals of the two countries were not more than 185 miles apart. The line of demarcation followed one of the many canals between the Tigris and Euphrates. It then crossed the Tigris and was formed by one of the rivers draining the Iranian table-land--the Upper Zab, the Radanu, or the Turnat. Each of the two states strove by every means in its power to stretch its boundary to the farthest limits, and the narrow area was the scene of continual war. Assyria was but a poor and insignificant country when compared with that of her rival. She occupied, on each side of the middle course of the Tigris, the territory lying between the 35th and 37th parallels of latitude. This was a compact and healthy district, well watered by the streams running from the Iranian plateau, which were regulated by a network of canals and ditches for irrigation of the whole region. The provinces thus supplied with water enjoyed a fertility which passed into a proverb. Thus Assyria was favoured by nature, but she was not well wooded. The most important of the cities were Assur, Arbeles, Kalakh and Nineveh. Assur, dedicated to the deity from which it took its name, placed on the very edge of the Mesopotamian desert, with the Tigris behind it, was, during the struggle with the Chaldæan power, exposed to the attacks of the Babylonian armies; while Nineveh, entrenched behind the Tigris and the Zab, was secure from any sudden assault. Thus it became the custom for the kings to pass at Nineveh the trying months of the year, though Assur remained the official capital and chief sanctuary of the empire, which began its aggrandisement under Assurballit, by his victory over the Cossæan kings of Babylon. But the heroic age comes before us in the career of Shalmaneser I., a powerful sovereign who in a few years doubled the extent of his dominions. He beautified Assur, but removed his court to Kalakh. His son, Tukulti-ninip I., made himself master of Babylon, and was the first of his race who was able to assume the title of King of Sumir and Akkad. This first conquest of Chaldæa did not produce lasting results, for the sons of the hero fought each other for the Crown, and Assyria became the scene of civil wars. The fortunes of Babylon rose again, but the depression of Assyria did not last long. Nineveh had become the metropolis. Confusion was increased in the whole of this vast region of Asia by the invasion and partial triumph of the Elamites over Babylon. But these were driven back when Nebuchadrezzar arose in Babylon. To Merodach he prayed, and "his prayer was heard," and he invaded Elam, taking its king by surprise and defeating him.