I think the explanation lies in the disposition of the marsh lands on the lower Thames. If you take the map of the Thames below the Isle of Dogs and mark upon it all that must have been primeval marsh (including much that is still marsh) you will see that wherever hard land is found upon one bank it is faced by extensive swamp upon the other. There was no good position for a permanent crossing even by ferry, and in the whole military history of England we only know one doubtful case in which a junction was effected from south to north, which is in the pursuit of the defeated British army by the Romans in A.D. 43 under Aulus Plautius. If, as is probable (though not certain), that battle took place at Rochester, then the pursuit was carried on by a direct crossing of the lower Thames; but with that exception I can call to mind no military action in the whole of our history where the lower Thames did not prove a permanent obstacle. It is an amusing speculation to think what would have happened to the road system of England if strategic necessity had appeared again during the modern period. The thing is purely hypothetical, but I might make a few suggestions. In the first place, we should certainly have had a road linking up the southern coast; next, we should certainly have had some form of continuous traffic over the lower Severn and the lower Thames and the Humber; next, without doubt, there would have been pierced a broad, continuous, and fairly direct road from the plain of Yorkshire to the plain of Lancashire across the Pennines; next, we should have had, of course, a broadening of all the ways leading to the main ports. That would have been essential, and particularly to the ports of the Straits of Dover. But, as I have said, the whole thing is a dream, because not that strategic motive, but now a purely economic motive is compelling us to revise our system. iv Apart from these two main causes of waterways, and of the absence of strategic necessity causing the diversion of the English Road, and apart from all other causes of local government which have led to such extraordinary diversity, lack of regular gradient, lack of regular gauge, etc. (as distinguished from the road system under the monarchical and centralized governments of the Continent, and especially of France), we have certain other elements which have stamped the English Road with its particular character. They may be briefly recapitulated without developing any one of them. We shall meet most of them again in the historical sketch of the English Road.