That a town would group up on the lowest crossing of the Thames, once that crossing with its bridge or ferry was definitely established, is obvious enough. That this town would be important and large if there were a sufficient development of population and culture in the island is equally obvious. Both consequences would naturally follow from the topography of Britain. But that this town should become of such high importance in the European scheme and of such overwhelming importance in the national scheme; further, that this town should soon grow to be the second town in size of Western Europe, and at last by far the first, is not so immediate a conclusion from the known topographical conditions which brought it into being. That moral and material growth of London is due, of course, to the supremacy which London enjoyed and enjoys as a place of _commerce_. It is London as a market, and as a market the port of which was the Thames, which we must next consider, and we must ask ourselves upon what so considerable and historical a phenomenon has been based. The matter is usually dismissed by an affirmation lacking analysis and still more lacking proof. Our text-books are too often satisfied with telling us that “the exceptionally favourable position of London as a commercial centre” was at the root of the town’s greatness. The affirmation is perfectly true, but it does not provide its own explanation nor satisfy our curiosity as to _why_ this position should have meant so much. I think, indeed, that most observant people in reading this or similar phrases must, if they had any knowledge of the map, have been struck with the apparent disadvantages under which a site such as that of London suffers. It has not behind it a vast hinterland from which it should be able to gather raw material for export, nor is it a natural outlet for the various products of several different regions as is, for instance, the region surrounding the mouths of the Rhine. It is not central to the European scheme as Lyons was for so many centuries, and Paris for so many centuries more. It lies a long way up its stream from the sea. No system of converging waterways unites in its neighbourhood. There seems at first sight, therefore, no reason why London should have obtained more than a local importance.