It is a commonplace which must be repeated whenever the connection of the Thames with London is referred to, that the capital matter in that connection is London’s position as _the lowest crossing point upon the Thames_. That affirmation, standing alone, is of no use to history unless one also explains why it was so important to find a crossing place as low as possible down the river, and the many causes which combine to make that lowest crossing place the neighbourhood of London Bridge. These last especially require a full explanation because, of the many converging reasons for selecting that site, the chief were, until quite recently, imperfectly studied. Why was it of such great importance for man, from the beginnings of a settled occupation in this island, to discover a convenient crossing place as low down as possible upon the course of the Thames? And why, when once this crossing place had been established, would it become the principal meeting-place in the country? The answer to these questions is to be found, not only in the shape of the island, but in the position of its best soil and in its relation to the Continent. [Illustration: HOUSES OF PARLIAMENT FROM VAUXHALL] It is obvious that the main connection between Great Britain and the Continent must be by the Straits of Dover. It is not only the shortness of the trajectory from the mainland to the island which makes the Straits of Dover the necessary and permanent entry into this country, it is a number of other things as well: as, that communication is very easy from the opposing shore inland; that that opposing shore was provided for ages with a harbour peculiarly suitable to early traffic--the Portus Itius (now the silted-up plain between the hills behind Boulogne); the conformation of the high land upon either side at Grinez and at Dover Cliffs which, in the centuries when the thing was important, gave an uninterrupted sight of land during the crossing; and the choice of entry which the various inlets (now filled up) afford from the Portus Lemanis behind Folkstone, the old inlet at Dover, and the old Mouth of the Stour to what was once the sheltered channel between Thanet and the mainland behind the island of Richborough. So powerful has been the topographical effect of the Straits that no revolution in travel has dispossessed them of their original importance. The great expansion in our means of communication has only emphasised the bond which is established by the Straits between this island and the Continent of Europe, and so throughout the whole of the old world. When, a few years hence, a man sets out to travel by land to India or to China, he will cross from Dover and will take his train at Calais. Were communication inland as uninterrupted throughout this island as it is throughout the opposing portion of the Continent, a system of roads would naturally have established itself, radiating from some depôt common to the various ports of Kent, just as a system