When the first group of Nordics arrived in this region, both they and their Alpine predecessors were ignorant of metal, but a few centuries later implements of copper began slowly to penetrate the whole area. Perhaps these arrived from the east, up the Danube valley, either from Hissarlik II. or from those Ægean merchants, who, as we have seen, were trading for Transylvanian gold, or taking copper axes to the Tripolje folk. Or it may be that other Ægean folk had by this time reached the head of the Adriatic, and were making their way thence to the mines of the Erz-gebirge and the amber coasts of the Baltic. It is probable that both lines of trade began fairly early in the third millennium, and the general course of the latter route can be traced in outline from Fiume, along the eastern foothills of the mountain zone towards Linz, where the Danube must have been crossed in dug-out canoes; thence it continued through the Elbe gap, and on by various routes, indicated by the distribution of flat celts, to the amber coast.[264] One thing is clear, and that is that metal reached the mountain zone from the east and not from the west. It was at one time believed that when metal first appeared in the western Mediterranean, the Rhone valley was the main line of approach into Central Europe.[265] This we now know was not the case,[266] for that valley was thickly wooded, and the inhabitants of most of it remained in a neolithic state until many centuries after metal had become known in Switzerland. After the destruction of Hissarlik II. communications from the east seem to have ceased for a time; the irruption of the steppe-folk appears to have interfered with trade, especially by land, over the north Ægean and Euxine areas. Perhaps, too, after the arrival of fresh hordes of steppe-folk into Hungary trade by the other route may also have ceased for a time. There is some evidence that this was the case, but in due course it was resumed, and was at any rate in full swing again long before 1600 /B.C./, though, judging by the type of weapons found, this trade was rather with Italy and the west than with the Ægean and the eastern Mediterranean. [Illustration: FIG. 8. GROOVED ITALIAN DAGGER FROM CASTELLANO, NEAR RIPATRANSONE.]