There is one last point to be considered in connection with London river as a port. It has been well made by Mr. Lyde in one of his short but remarkable geographical studies. The estuary of the Thames exactly faces that great and permanent frontier line between two parts of our European culture, upon either side of which lie contrasting speeches, traditions, and even religions. That frontier roughly divides such areas of Western Europe as have continuously preserved the traditions of the Roman Empire from outer regions to the east and to the north, which only received the Christian religion and the Roman civilisation after the breakdown of central authority exercised from the Imperial city. The estuary of the Thames opens like a funnel just opposite the point where this frontier between what some would call the “Teutonic” and “Latin” areas, reaches the sea. It may not be at first sight apparent why a position of this kind is of capital commercial importance. The reason is rather moral than material, though it has its material element in the cheapness and expedition of carriage by sea. Areas which differ in the type of their culture tend to become polarised one towards the other for the purposes of exchange. Each will tend to produce something that the other lacks. Now the exchange between two such areas will, of course, proceed actively enough across innumerable points lying upon the frontier between them, but it will not penetrate very far inland, if there is in competition with the inland routes a water route. Thus Arras will exchange easily enough with, say, Aix-la-Chapelle, Metz with Trèves or Frankfort, but what of Rouen and the Baltic, Bordeaux and the Frisian Lowlands, Brittany and Vendée and the German Plain? It is evident that if no friction existed a direct sea-borne commerce along the north-western coasts of Europe would effect these exchanges; but there does exist a friction, especially in early times, consisting in the ignorance and, as it were, the credulity, separating places so far distant in mileage and, what is more important, in culture. If, then, a half-way house is found sufficiently familiar to either party, that half-way house will tend to become in this new aspect out of so many, a centre of exchange--and this is precisely what happened to London. The North Sea and the Baltic were familiar with London--but then so was the Channel and the Bay of Biscay. London river attracted in this fashion a sheaf of trade routes, drawn from the north and east, another from the south and west. And so true is this that to the present day, and in one curious slight but emphatic modern instance, you can see the process at work. Travellers intent upon no purpose of commerce but merely upon an excursion will leave London river for Boulogne and Calais, sometimes for Dieppe and Havre; other travellers will leave the same facility of egress for the Scheldt and the Rhine and the Dutch ports and the Elbe.