and in the horned cairns of the north of Scotland.  These parallels are due to something more than coincidence; in fact, it is clear that megalithic building is a widespread and homogeneous system, which, despite local differences, always preserves certain common features pointing to a single origin.  It is thus difficult to accept the suggestion that it is merely a phase through which many races have passed.  The phases which occur in many races alike are always those which are natural and necessary in the development of a people, such as the phase of using copper.  But there is nothing either natural or necessary in the use of huge unwieldy blocks of stone where much smaller ones would have sufficed.

There are further objections to this theory in the distribution of the megalithic buildings both in space and time.  In space they occupy a very remarkable position along a vast sea-board which includes the Mediterranean coast of Africa and the Atlantic coast of Europe.  In other words, they lie entirely along a natural sea route.  It is more than accident that the many places in which, according to this theory, the megalithic phase independently arose all lie in most natural sea connection with each other, while not one is in the interior of Europe.

In time the vast majority of the megalithic monuments of Europe seem to begin near the end of the neolithic period and cover the copper age, the later forms continuing occasionally into that of bronze.  Here again it is curious that megalithic building, if merely an independent phase in many countries, should arise in so many at about the same time, and with no apparent reason.  Had it been the use of worked stones that arose, and had this followed the appearance of copper tools, the advocates of this theory would have had a stronger case, but there seems to be no reason why huge unworked stones should simultaneously begin to be employed for tombs in many different countries unless this use spread from a single source.

For these reasons it is impossible to consider megalithic building as a mere phase through which many nations passed, and it must therefore have been a system originating with one race, and spreading far and wide, owing either to trade influence or migration.  But can we determine which?

Great movements of races by sea were not by any means unusual in primitive days, in fact, the sea has always been less of an obstacle to early man than the land with its deserts, mountains, and unfordable rivers.  There is nothing inherently impossible or even improbable in the suggestion that a great immigration brought the megalithic monuments from Sweden to India or vice versa.  History is full of instances of such migrations.  According to the most widely accepted modern theory the whole or at least the greater part of the neolithic population of Europe moved in from some part of Africa at the opening of the neolithic age.  In medieval history we have the example of the Arabs, who in their movement covered a considerable portion of the very megalithic area which we are discussing.