Now when we recognise that the bulk of English wealth lay for centuries south and east of a line drawn from Exmouth to the Wash, and when we appreciate what the Thames valley is in that triangle, we shall see how necessarily the main market of the Thames was also the main market of England. The natural water communications of the south consist in a number of small streams, only one of which, the Salisbury Avon, may have been navigable for more than a dozen miles or so inland. East Anglia was better served, and particularly the northern area, which was drained by the three rivers converging upon Breydon Water. The northern part of that area was also fairly well served by the three parallel rivers of the Ouse, the Nen, and the Welland, but their service as a means of communication was handicapped by the nature of their entry into the sea through the Fens, and after that through the perils, sandbanks, and shallows of the Wash; while the good service of rivers along all the East Anglian coast had this drawback: that, as we there have nothing but a series of short systems, there was no water connection between one group of short valleys and another, not even one thought-out road. A dozen streams will carry produce from the sea to Worstead, to Norwich, to Beccles, to what was once the considerable port of Orford, to Ipswich, to Colchester, etc. But each avenue is a separate avenue. There is no “trunk” connecting the system. With the Thames it is otherwise. Glance down the valley and see how one point after another, each the natural market of a whole district of its own, drains the produce from the north and the south of the river, to discharge it upon the main stream. From Lechlade (up to which point ran the “measure and the bushel of London”)[4] through Oxford, Abingdon, Wallingford, Reading, Marlow, the Middle Hythe (which we now call Maidenhead), and Windsor, you have a whole string of such centres, each gathering its own section’s produce from its scheme of roads, or of subsidiary streams, and turning the mass down seaward upon the “trunk” afforded by the Thames. The Thames, therefore, with London as its port of transhipment between the inland communications and the sea, tapped the very heart of all that was wealthiest in England for fifteen hundred years, and all that commerce by river as by road drained upon London because London was “central” to exchange in the rich south and east of the island. But, as we have seen, two further characters were attached to “draining” power. We must not only seek a point central for communications, we must also seek a point where there was a ready demand for import and a ready access to the best foreign markets. Let us consider these two characters in their order: