It thus seems that the most probable theory of the origin of the megalithic monuments is that this style of building was brought to the various countries in which we find it by a single race in an immense migration or series of migrations.  It is significant that this theory has been accepted by Dr. Duncan Mackenzie, who is perhaps the first authority on the megalithic structures of the Mediterranean basin.

One question still remains to be discussed.  From what direction did megalithic architecture come, and what was its original home?  This is clearly a point which is not altogether dependent on the means by which this architecture was diffused.  Montelius speaks in favour of an Asiatic origin.  He considers that caves, and tombs accessible from above, i.e. simple pits dug in the earth, were native in Europe, while tombs reached from the side, such as dolmens and corridor-tombs, were introduced into Europe from the east.  Salomon Reinach, arguing mainly from the early appearance of the objects found in the tombs of Scandinavia and the rarity of the simpler types of monument, such as the dolmen, in Germany and South Europe, suggests that megalithic monuments first appeared in North Europe and spread southwards.  Mackenzie is more inclined to believe in an African origin.  If he is right it may be that some climatic change, possibly the decrease of rainfall in what is now the Sahara desert, caused a migration from Africa to Europe very similar to that which many believe to have given to Europe its early neolithic population.  The megalithic people may even have been a branch of the same vast race as the neolithic:  this would explain the fact that both inhumed their dead in the contracted position.

It is probable that the problem will never be solved.  The only way to attempt a solution would be to show that in some part of the megalithic area the structures were definitely earlier than in any other, and that as we move away from that part in any direction they become later and later.  Such a means of solution is not hopeful, for the earliest form of structure, the dolmen, occurs in all parts of the area, and if we attempt to date by objects we are met by the difficulty that a dolmen in one place which contained copper might be earlier than one in another place which contained none, copper having been known in the former place earlier than in the latter.

It still remains to consider the question of the origin of the rock-hewn sepulchre and its relation to the megalithic monument.  The rock-tomb occurs in Egypt, Phoenicia, Rhodes, Cyprus, Crete, South Italy, Sicily, Sardinia, Malta, Pianosa, the Iberian Peninsula, the Balearic Isles, and France.  In all these places there are examples which are certainly early, i.e. belong to the neolithic or early metal age, with the exception of Malta and perhaps Rhodes and Phoenicia.  Two types are common, the chamber cut in the vertical face of rock and thus entered