enjoys freedom from taxation and unrestricted use of the rivers and fisheries.  To vary their scant and monotonous diet, they construct floating gardens on rafts of bamboo covered with earth, on which they plant onions and garlic and which they tow behind their boats.  They also raise hundreds of ducks, which are trained to go into the water to feed and return at a signal,[594] thus expanding the resources of their river life.  Bangkok has all its business district afloat on the Menam River—­shops, lumber yards, eating-houses and merchants’ dwellings.  Even the street vendor’s cart is a small boat, paddled in and out among the larger junks.[595]

A far more modern type of river-dwellers is found in the “shanty-boat” people of the western rivers of the United States.  They are the gypsies of our streams, nomads who float downstream with the current, tying up at intervals along the bank of some wooded island or city waterfront, then paying a tug to draw their house-boat upstream.  The river furnishes them with fish for their table and driftwood for their cooking-stove, and above all is the highway for the gratification of their nomad instincts.  There is no question here of trade and overpopulation.

[Sidenote:  Reclamation of land from the sea.]

Pile dwellings and house-boats are a paltry form of encroachment upon the water in comparison with that extensive reclamation of river swamps and coastal marshes which in certain parts of the world has so increased the area available for human habitation.  The water which is a necessity to man may become his enemy unless it is controlled.  The alluvium which a river deposits in its flood-plain, whether in some flat stretch of its middle course or near the retarding level of the sea, attracts settlement because of its fertility and proximity to a natural highway; but it must be protected by dikes against the very element which created it.  Such deposits are most extensive on low coasts at or near the river’s mouth, just where the junction of an inland and oceanic waterway offers the best conditions for commerce.  Here then is a location destined to attract and support a large population, for which place can be made only by steady encroachment upon the water of both river and sea.  Diking is necessitated not only by the demand for more land for the growing population, but also by the constant silting up of the drainage outfalls, which increases the danger of inundation while at the same time contributing to the upbuilding of the land.  Conditions here institute an incessant struggle between man and nature;[596] but the rewards of victory are too great to count the cost.  The construction of sea-walls, embankment of rivers, reclamation of marshes, the cutting of canals for drains and passways in a water-soaked land, the conversion of lakes into meadow, the rectification of tortuous streams for the greater economy of this silt-made soil, all together constitute the greatest geographical transformation that man has brought about on the earth’s surface.[597]