Perhaps, at first sight, one of the most striking things in all this stretch of the River is the absence of ancient fortifications. True, we have those at Sheerness, but they were made for the guarding of the dockyard and of the approach to the important military centre at Chatham, which lies a few miles up the River Medway. Surely this great opening into England, the gateway to London, this key to the entire situation, should have had frowning castles on each shore to call a halt to any venturesome, invading force. Thus we think at once with our twentieth-century conception of warfare—forgetting that the cannon of early days could never have served to throw a projectile more than a mere fraction of the distance across the stream. Not till we pass up the Lower Hope and Gravesend Reaches and come to Tilbury and Gravesend, facing each other on the two banks, do we reach anything like a gateway. Then we find Tilbury Fort on the Essex shore, holding the way upstream. Here, at the ferry between the two towns, the River narrows to less than a mile in width; consequently the artillery of ancient days might have been used with something like effectiveness. [Illustration: _Training Ships off Greenhithe._ “Arethusa” for Homeless Boys “Worcester” Nautical Training College] From Gravesend westwards the country still lies very low on each bank, but the monotony is not quite so continuous, for here and there, first at one side and then at the other, there rise from the widespread flats little eminences, and on these small towns generally flourish. At Northfleet and Greenhithe, for instance, where the chalk crops out, and the River flows up against cliffs from 100 to 150 feet high, there is by contrast quite a romantic air about the place, and the same may be said of the little town of Purfleet, which lies four miles up the straight stretch of Long Reach, its wooded chalk bluffs with their white quarries very prominent in the vast plain. But, for the most part, it is marshes, marshes all the way, particularly on the Essex shore—marshes where are concocted those poisonously unpleasant mixtures known as “London specials,” the thick fogs which do so much to make the River, and the Port as well, a particularly unpleasant place at certain times in winter. When a “London special” is about—that variety which East Enders refer to as the “pea-soup” variety—the thick, yellow, smoke-laden mist obscures everything, effectively putting an end to all business for the time being.