The conditions which give a river this great historic importance, the fundamental character, therefore, which has lent to the Thames its meaning in English history, is twofold: a river affords a permanent means of travel, and a river also forms an obstacle and a boundary. Men are known to have agglomerated in the beginning of society in two ways: as nomadic hordes and as fixed inhabitants of settlements.
There has arisen a profitless discussion as to which of these two phases came first. No evidence can possibly exist upon either side, but one may take it that with the first traditions and records, as at the present time, the two systems existed side by side, and that either was determined by geographical conditions. A river is an advantage to both groups, but to the second it is of more consequence than to the first; and in South England, if we go back to the origins of our history, it is in fixed settlements that we find the first evidence of man. With every year of research the extreme antiquity of our inhabited sites becomes more apparent. And indeed the geographical nature of Southern England should make us certain of the antiquity of village life in it, even were there no archæological evidence to support that antiquity.
South England is everywhere fertile, everywhere well watered, and nowhere divided, as is the North, by long districts of bare country, or of hills snowbound in winter, or of morass. Its forests, though numerous, have never formed one continuous belt; even the largest of them, the Forest of the Weald, between the downs of Surrey and Kent and those of Sussex, was but twenty miles across--large enough to nourish a string of hunting villages upon the north and the south edges of it; but not large enough to isolate the Thames Valley from the southern coast.
From the beginning of human activity in this island the whole length of the river has been set with human settlements never far removed one from the other; for the Thames ran through the heart of South England, and wherever its banks were secure from recurrent floods it furnished those who settled on them with three main things which every early village requires: good water, defence, and communication.