The key role of water transportation before the construction of railroads
is evident in the great economic significance of canals, where the draft power
was often the same—horses, mules, oxen—but the reduction of friction made
possible by barges moving over water allowed for huge gains in efficiency.
River or sea transportation takes advantage of “routes of least friction,” of
least geographical resistance, and thereby vastly extends the distances over
which food supplies, salt, arms, and people can be exchanged. In epigrammatic
form, we could say that “easy” water “joins,” whereas “hard” hills,
swamps, and mountains “divide.”