We have now reached a period at which the population of Europe becomes greatly mixed, in consequence of the constant rovings and incursions of the various races and tribes of which it was composed. It is interesting to note the effect of such a state of things upon the physical characteristics of the people. And first it is to be observed, that, with extremely rare exceptions, conquest is not attended by extermination. When one people, even in semi-barbarous times, conquers another, it does not annihilate and rarely displaces, but for the most part only overlays it. The annihilating process, of which a sample may be seen in America, only takes place in the rare case of the meeting of two nations, in such widely different states of civilisation as to render amalgamation impossible,—and even in this case only when the inferior race is so intractable as to resist all obedience to the superior. _Displacement_—which is obsolete now, since advancing civilisation has rendered conquest political only—was pretty common two thousand years ago, when Europe was thinly and nomadically peopled, and tribes migrated _en masse_. In this way, for example, the Cimbri wedged themselves in among the Celts in Northern Gaul, and took possession of a large tract in Northern Italy. But soon after the Christian era—chiefly in consequence of the increasing density and settled habits of the population—conquest ceased to produce either extermination or displacement, and consisted merely in the overlaying of one population by another much less numerous but more powerful. Thus the Normans in England and the Franks in Gaul were but a handful compared to the conquered population; and consequently, though they might give their laws and even their name to the country, they could not materially alter the physical character of the people.