When we consider something more than distance and think of London as the “centre of gravity” of the Midlands, the east and the south, we find it still more central for the centuries immediately preceding our own. Their staple export was wool. The pasturage of the chalk ranges runs right round London in the Chilterns and their extension into East Anglia, in the north and south Downs and the Uplands of Wiltshire, Hampshire, and Dorset. London is the obvious centre of all that triangle of chalk. It is again nearly equi-distant from the principal markets of Norfolk, of the Upper Trent valley, of Dorset, and of the Cotswolds. If we treat as exceptions the Lancashire and Yorkshire Plains (each with their local ports), the Vale Royal and the Lower Severn (each with its local port at Chester and at Bristol), London is very near the commercial centre of gravity of what remains. We must not forget that the Marlborough Downs and Salisbury Plain are but a few miles more distant from London Bridge than is the extremity of Kent. From the town of Pewsey to London Bridge as the crow flies is almost exactly eighty-eight miles. From the South Foreland the distance is not ten miles less. It needs but a slightly longer radius to include all the Warwickshire Midlands and very nearly all the county of Norfolk: all, of course, of Suffolk, of Essex, of Kent, Sussex, Surrey, and Hampshire. London is geographically and commercially central at any rate to the older England--which was all that was needed for its establishment. It was even more central when regarded as a nexus of communications. How all the main roads centred there we have already seen. The roads alone would have given London a pre-eminence as a market above all other towns in Britain even if the Thames had dried up after their establishment. But the position was meanwhile further strengthened by the conditions of water carriage; and it is here that the meaning of the Thames as a whole appears, and the way in which the upper as well as the lower river has built up the greatness of London. I have no space to show why and how water carriage was of supreme importance both in primitive times (that is, before the Roman civilisation came) and during the Dark Ages through which, in spite of decline, it survived. It should be sufficient to point out that in the decline of a civilisation, or in its absence, water carriage--suited to heavy burdens, requiring no repair of ways, and providing a mode of traction ready-made--is, wherever it is available, the chief economic factor of commerce.