the heart of the empire.  Even if Cilicia and Syria should be conquered, nothing was easier than to oppose a further advance at the barrier of the Euphrates; and should the Euphrates be crossed, the Khabur still remained, and behind it the desert of Singar, which offered the last obstacle between Nineveh and the invaders.  The distances were less considerable in the case of an army setting out from Urartu and proceeding along the basin of the Tigris or its affluents; but here, too, the difficulties of transit were so serious that the invader ran a great risk of gradually losing the best part of his forces on the road.  On the north-east and east, however, the ancient heritage of Assur lay open to direct and swift attack.  An enemy who succeeded in destroying or driving back the garrisons stationed as outposts on the rim of the plateau, from Kharkhar to Parsua, if he ventured to pursue his advantage and descended into the plain of the Tigris, had no less than three routes to choose from—­the Kirind road on the south, the Baneh road on the north, and the Suleimanych road between the two.  The last was the easiest of all, and led almost straight to the fords of Altun-Keupri and the banks of the Lesser Zab, on the confines of Assyria proper, close under the walls of Arbela, the holy city of Ishtar.

[Illustration:  300.jpg THE ASSYRIAN TRIANGLE]

He needed but to win two victories, one upon leaving the mountains, the other at the passage of the Zab, and two or three weeks’ steady marching would bring him from Hamadan right up to the ramparts of Nineveh.  Cyaxares won a victory over Assur-bani-pal’s generals, and for the first time in over a hundred years Assyria proper suffered the ignominy of foreign invasion.  The various works constructed by twenty generations of kings had gradually transformed the triangle enclosed between the Upper Zab, the Tigris, and the Jebel-Makhlub into a regular fortified camp.  The southern point of this triangle was defended by Calah from the attacks of Chaldoa or from foes coming down from Media by Iiolwan and Suleimanyeh, while Nineveh guarded it on the northeast, and several lines of walled cities—­among which Dur-Sharrukin and Imgur-Bel can still be identified—­protected it on the north and east, extending from the Tigris as far as the G-hazir and Zab.  It was necessary for an enemy to break through this complex defensive zone, and even after this had been successfully accomplished and the walls of the capital had been reached, the sight which would meet the eye was well calculated to dismay even the most resolute invader.  Viewed as a whole, Nineveh appeared as an irregular quadrilateral figure, no two sides of which were parallel, lying on the left bank of the Tigris.

[Illustration:  301.jpg MAP OF NINEVEH]

The river came right up to the walls on the west, and the two mounds of Kouyunjik and Nebi-Yunus, on which stood the palaces of the Sargonides, were so skilfully fortified that a single wall connecting the two sufficed to ward off all danger of attack on this side.  The south wall, which was the shortest of the four, being only about 870 yards in length, was rendered inaccessible by a muddy stream, while the north wall, some 2150 yards long, was protected by a wide moat which could be filled from the waters of the Khuzur.