rivers, the supply of food in time of scarcity or of succour in time
of danger is never secure: a little narrow path kept up by nothing but
the continual passage of men and animals is all the channel a
community of men have for communicating with their neighbours by land.
And it must be remembered that upon such communication depend not only
the present existence, but the future development of the society,
which cannot proceed except by that fertilisation, as it were, which
comes from the mixture of varied experiences and of varied traditions:
every great change in history has necessarily been accompanied by some
new activity of travel.

Under the primitive conditions of which we speak a river of moderate
depth, not too rapid in its current and perennial in its supply, is
much the best means by which men may communicate. It will easily
carry, by the exertions of a couple of men, some hundred times the
weight the same men could have carried as porters by land. It
furnishes, if it is broad, a certain security from attack during the
journey; it will permit the rapid passage of a large number abreast
where the wood tracks and paths of the land compel a long procession;
and it furnishes the first of the necessities of life continually as
the journey proceeds.

Upon all these accounts a river, during the natural centuries which
precede and follow the epochs of high civilisation, is as much more
important than the road or the path as, let us say, a railway to-day
is more important than a turnpike.

What is equally interesting, when a high civilisation after its little
effort begins to decline into one of those long periods of repose into
which all such periods of energy do at last decline, the river