The question thus raised has been keenly debated since.  At the Stockholm Congress in 1874 de Mortillet advanced the theory that megalithic monuments in different districts were due to different peoples, and that what spread was the custom of building such structures and not the builders themselves.  This theory has been accepted by most archaeologists, including Montelius, Salomon Reinach, Sophus Mueller, Hoernes, and Dechelette.  But while the rest believe the influences which produced the megalithic monuments to have spread from east to west, i.e. from Asia to Europe, Salomon Reinach holds the contrary view, which he has supported in a remarkable paper called Le Mirage Oriental, published in 1893.

The questions we have to discuss are, therefore, as follows:  Are all the megalithic monuments due to a single race or to several?  If to a single race, whence did that race come and in what direction did it move?  If to several, did the idea of building megalithic structures arise among the several races independently, or did it spread from one to another?

We shall consider first the theory that the idea of megalithic building was evolved among several races independently, i.e. that it was a phase of culture through which they separately passed.

On the whole, this idea has not found favour among archaeologists.  The use of stone for building might have arisen in many places independently.  But megalithic architecture is something much more than this.  It is the use of great stones in certain definite and particular ways.  We have already examined what may be called the style of megalithic architecture and found that the same features are noticeable in all countries where these buildings occur.  In each case we see a type of construction based on the use of large orthostatic slabs, sometimes surmounted by courses of horizontal masonry, with either a roof of horizontal slabs or a corbelled vault.  Associated with this we frequently find the hewing of underground chambers in the rock.  In almost all countries where megalithic structures occur certain fixed types prevail; the dolmen is the most general of these, and it is clear that many of the other forms are simply developments of this.  The occurrence of structures with a hole in one of the walls and of blocks with ‘cup-markings’ is usual over the whole of the megalithic area.  There are even more remarkable resemblances in detail between structures in widely separated countries.  Thus the Giants’ Tombs of Sardinia all have a concave facade which forms a kind of semicircular court in front of the entrance to the tomb.  This feature is seen also in the temples of Malta, in the tomb of Los Millares in Spain, in the naus of the Balearic Isles (where, however, the curve is slight), in the Giant’s Grave of Annaclochmullin and the chambered cairn of Newbliss in Ireland, in the tomb of Cashtal-yn-Ard in the Isle of Man, in the barrow of West Tump in Gloucestershire,