It embraced also the upper basin of the Pyramos and its affluents, as well as the regions situated between the Euphrates and the Halys, but its frontier in this direction was continually fluctuating, and our researches fail to follow it. It is somewhat probable that it extended considerably towards the west and north-west in the direction of the AEgean Sea. The forests and escarpments of Lycaonia, and the desolate steppes of the central plateau, have always presented a barrier difficult to surmount by any invader from the east. If the Khati at that period attacked it in front, or by a flank movement, the assault must rather have been of the nature of a hurried reconnaissance, or of a raid, than of a methodically conducted campaign.* * The idea of a Hittite empire extending over almost all Asia Minor was advanced by Sayce. They must have preferred to obtain possession of the valleys of the Thermodon and the Iris, which were rich in mineral wealth, and from which they could have secured an inexhaustible revenue. The extraction and working of metals in this region had attracted thither from time immemorial merchants from neighbouring and distant countries--at first from the south to supply the needs of Syria, Chaldaea, and Egypt, then from the west for the necessities of the countries on the AEgean. The roads, which, starting from the archipelago on the one hand, or the Euphrates on the other, met at this point, fell naturally into one, and thus formed a continuous route, along which the caravans of commerce, as well as warlike expeditions, might henceforward pass. Starting from the cultivated regions of Maeonia, the road proceeded up the valley of the Hermos from west to east; then, scaling the heights of the central plateau and taking a direction more and more to the north-east, it reached the fords of the Halys. Crossing this river twice--for the first time at a point about two-thirds the length of its course, and for the second at a short distance from its source--it made an abrupt turn towards the Taurus, and joined, at Melitene, the routes leading to the Upper Tigris, to Nisibis, to Singara, and to Old Assur, and connecting further down beyond the mountainous region, under the walls of Carchemish, with the roads which led to the Nile and to the river-side cities on the Persian Gulf.* * The very early existence of this road, which partly coincides with the royal route of the Persian Achemenids, was proved by Kiepert.