We find the Slavs especially spreading over this fertile heart of Russia about the eighth century of the present era. The land had long been held by the Finns and other Asiatic tribes when, in the third century, the Goths from the north fell upon them and drove them eastward. In the next century began that more formidable invasion from Asia which flung the Finns westward once more, and cast the Teutons upon the crumbling barrier of the Roman Empire. In the seventh century a new semi-civilised race, the Khazars, created an empire in south-eastern Russia, and drove the Asiatic Finns definitely to the north. It was at the close of these great movements that the Slavs moved rapidly over the fertile regions, between the land of the Finns and the southern kingdom of the Khazars, By the end of the eighth century the various Slav tribes had overrun the central part of western Russia. The chief change which this migration caused in the life of the Slavs was the development of commerce. The great rivers of the land at once became the highways. Fishers as well as tillers of the soil, the Slavs would spread along the river-valleys, and the junctions of the rivers would naturally become the chief stations for what intercourse there was between the scattered villages. It is probable that in those days, when four-fifths of Russia was marsh and forest, the rivers were deeper than they are to-day. In our time they are for the most part shallow throughout the summer. Only in the spring, when the melting snows and rains flush the broad channels, can large boats ascend them; and in the winter their frozen waters make good passage for the sledge. They became the high-roads of the new commonwealth, as the site of the older cities indicates when one glances at the map. The Slavs had at that time probably little or no commerce. Some exchange, in kind, of fish, fur, honey, or corn might take place, but the resources were much the same for each village. In a short time after the settlement, however, a busy commercial system was inaugurated. Further north than the Finns were the Scandinavians, whose skill in metal-working was early developed. The Slavs traded with them for swords and spears and axes.