2. 820: Spread of the Norsemen
By making their headquarters at Aix-la- Chapelle (Aachen) the Carolingians had contributed to a first awakening of the region, which was interrupted by the ravages of the Norsemen
In the eighth and ninth centuries, the limits of a northern maritime empire had already been staked out and sometimes exceeded by the expeditions, invasions and piracy of the Norsemen. Their venture may have become dispersed over the broad spaces and coastlines of Europe, but something of it remained in its place of origin. For some time afterwards, Scandinavian longboats ranged the North Sea and the Baltic - the Norwegians went to the English coast and the Irish Sea; the peasants of Gotland sailed into ports and rivers as far away as Novgorod; from Jutland to Finland there sprang up the Slavonic towns whose remains are now being uncovered by archaeologists; Russian merchants reached Stettin, hitherto a completely Slav town.   But there was no truly international economy before the Hanseatic League. Gradually, peaceably, thanks to trading and agreements with princes, but with the occasional use of force and violence too, this double sea- space, the North Sea and the Baltic, was taken in hand and organized by the cities, merchants, soldiers and peasants of Germany.
Europe expanded in many directions which followed the great Nordic migrations of the fifth century, as settlement of the ‘Norsemen’ extended beyond the boundaries of the Roman Empire towards Germany and eastern Europe, Scandinavia and the only partly- Romanized British Isles. Gradually the seas surrounding the old continent - the stretch of water encompassing the Baltic, the North Sea, the English Channel and the Irish Sea - were colonized. Here too, the 'new West' went beyond what Rome had accomplished: despite her fleets based at the mouth of the Somme and at Boulogne, Rome had never really ruled these northern waves.
Nevertheless, most important frontier in European expansion was the internal frontier of forest, marsh and heath.  The uninhabited wastes were reduced in size as the European peasants cleared the land; as people became more numerous, they harnessed the power of wheel and windmill; communications were established between regions once completely foreign to each other; barriers came down; countless towns sprang up or revived wherever there was a crossroads of trade, and this was undoubtedly the crucial factor. Europe was suddenly covered with towns - more than 3000 in Germany alone. Some of them, it is true, were little more than villages, despite their city walls, harbouring a mere two to three hundred souls. But many of them grew to become towns of a new and unprecedented kind.
Classical antiquity had had its free cities, the Greek city-states; but these had been open to the inhabitants of the surrounding countryside, who were free to come and go as they pleased. The west European medieval town was on the contrary a closed citadel behind its walls. 'The wall separates the townsman from the peasant', as a German proverb says. The town was a world of its own, protected by its privileges (`the city air makes men free'), an aggressive world and an active force for unequal exchange. And it was the medieval city - a more or less active ferment depending on period and place -  which, like the yeast in some mighty dough, brought about the rise of Europe. Can the prominent role of the city be accounted for by its having been able to expand and develop in an already- structured rural world, rather than in a vacuum like the towns of the New World (and possibly the Greek city- states themselves)? In other words, it had ecological material available to work on, at the expense of which it could grow. What was more, the territorial state, since it took so long to appear on the scene, offered no competition and easily and predictably outstripped the slower developments of the more impoverished south.