Once that crossing was founded and continuously maintained it was equally necessary that it should grow into the chief meeting place of the island; that is, the chief market and therefore the chief town. Indeed the various advantages such a crossing would have form so rare a combination that we should be perfectly justified, even if we had not the evidence we have, in making certain of the existence of a great and important London early in history. All the causes which we have seen to feed the commercial growth of the site from the sea were reinforced by the inland communications which met at this crossing place. The bridge (as I have shown elsewhere) made a terminal not only to sea-borne traffic, but to all the inland traffic from down the upper valley. It became the place of transhipment. It was further the terminal, and the necessary terminal, of the three great roads from north-west, from the north, and from the east, which combined at this point to seek the Straits of Dover to the south; and once this nexus was woven, once the market and place of meeting was fixed, it must further become the goal of other roads against which the Thames did not originally provide an obstacle. Thus it was that a road would necessarily be established from this crossing place to the west and to the south-west. Though the main traffic from the fertile Lower Severn valley would more naturally make for the Straits by way of the Chalk ridges, yet, when once London with its market supplies and depôts was established, a main road would necessarily aim at the Straits _through_ London rather than south of the Thames. And though the secondary entries into the island from the Continent by Southampton Water, and by the ports to the west of it, would naturally send out arteries of communication northward and westward, yet their communication north-eastward through London would soon acquire the chief place. That London would have become what it did through no more than these domestic causes may well be denied. The main factor in its growth was throughout the centuries what it remains to-day--the commerce of the tidal Thames. But standing at the head of that commerce London also gathered to itself, as the main crossing point of the Thames, the communications of the whole island. The peculiar and determining effect this had upon the military history of England I have mentioned in another study,[1] and shall expand in this. Parallel effects could be found in every other department of activity, not only in commerce but in the political machinery of England, of English feudalism, and of the English monarchy, and later of English aristocratic government. London once so formed upon its river was the centre or support of each in turn supreme in the island.