We must not exaggerate the point, for the strategy of the time was very confused, and sometimes at first almost purposeless; but none the less in any campaign, however muddled, the main natural strategy imposed by topography invariably appears, and for what it is worth I cite it in this case of the Lower Thames and of the Civil Wars. The third point, of course, in this connection of the Lower Thames with the Civil Wars waged in this island is the position of London: and that position is twofold. London has one great strategical character as the lowest crossing place of the Thames; it has another great strategical character as the chief natural base in the island. The first of these two characters is obvious, and as obviously recurs throughout the whole history of battle between the Norman Conquest and the Parliamentary Wars. Whoever has possession of London has possession of the secure crossing place nearest the sea which gives immediate interior communication between one section of the east of the island and the other, and as a rule to have possession of London is to have command sooner or later of the whole of the south and east upon that account. But the second character, London as a base, is of even more importance. You had here a town so great that after the Dark Ages it need never stand a siege. It is further a town the supplies of which under primitive conditions lay almost always uncut. Unless a man had so considerable a fleet that he could cut off supplies by River, so well organised a transport that he could keep both banks of that broad stream perpetually in touch, and finally so very large a command that he could hold the whole circuit of the walls securely and the Bridge end on the Southwark side as well, London could not be, strictly speaking, besieged, and, from the Danish Wars onwards, London never was.