INTRODUCTION TO SOCIOLOGY 4"
frontiers tended to become independent of the internal adminis- trative and governmental divisions, and to overstep the military and political frontiers of the empire. This, indeed, is evidence that there are other frontiers than the latter. I add that even religious or moral frontiers are not purely ideological, but imply a temporal constitution.
Like the Christian invasion, that of the barbarian peoples was slow, but irresistible. It was often and at first an obscure and apparently peaceful infiltration. Gradually they were admitted either as colonies, or as mercenaries with their chiefs. These chiefs ended by taking high military rank, and being charged with the defense of the empire against new invaders. In the fourth and fifth centuries the invasions became more violent; they harassed both the East and the West. Beginning with the end of the fifth century, the Visigoths made themselves masters of Spain and of Gaul ; of the latter as far as the Loire, and of the former the whole except the region included between the Duero on the south and the ocean on the west, where the Suevi set up a kingdom. The kingdom of Burgundy included almost all of the basin of the Rhone, where, however, Provence was held by the Visigoths. It is seen that these new states were not bounded by rigorous physical frontiers. They embraced one or several basins and mountain regions.
The kingdom of the Franks extended from the ocean on the west to the lower course of the Rhine on the north, and along the whole middle basin of the Rhine on the east and of the upper Rhine on the southeast. Burgundy, to the south of the Prankish kingdom, occupied the sources of the Seine, of the Marne, and of the Meuse. One can therefore no longer say that these peoples occupied one or more basins which naturally confined them within these limits. Mountains, rivers, and basins may occasionally be adapted as frontiers, but only to the extent to which they may temporarily correspond to the internal state of the forces of a society relative to surrounding forces. The kingdom of the Franks included the mouths and the greater part of the basins of the Seine, the Scheldt, the Marne, the Meuse, the Moselle, and the Rhine.
