ry, had their cabins
dispersed over the low deltaic land on earthen mounds made by their own
hands. There is also strong evidence that some of the works of the
Mound-builders in the "bottoms" of the middle and lower Mississippi
served as protected sites for the dwellings of their chiefs.[607]

[Sidenote: Diking of rivers.]

Such meager provisions against inundation suffice for the sparse
population characterizing the lower stages of civilization, but they
must be supplemented for the increasing density of higher stages by the
embankment of the stream, to protect also the adjacent fields. Hence the
process of confining rivers within dikes goes back into gray antiquity.
Those of the Po and its tributaries were begun before the political
history of the Lombardy plains commenced. Strabo mentions the canals and
dikes of Venetia, whereby a part of the country was drained and rendered
tillable.[608] The main Po has been embanked for centuries as far up as
Cremona, a distance of 600 miles, and the Adige to Verona.[609] But the
most gigantic dike system in the world is that of the Hoangho, by which
a territory the size of England is won from the water for
cultivation.[610] The cost of protecting the far spread crops against the
autumn floods has been a large annual expenditure and unceasing
watchfulness; and this the Chinese have paid for two thousand years, but
have not always purchased immunity. Year by year the Yellow River mounts
higher and higher on its silted bed above the surrounding lowlands,
increasing the strain on the banks and the area of destruction, when its
fury is uncaged. The flood of 1887 covered an area estimated at 50,000
square miles, wiped out of existence a million people, and left a
greater number a prey to famine.[611] So the fertile Chengtu plain of the
Min River, supporting four millions of people on its 2,500 square miles
of area, owes its prosperity to the embanking and irrigating works of
the engineer heroes, Li Ping and his son, who lived before the Christian
era. On the temple in their honor in the city of Kuan Hsien is Li Ping's
motto, incised in gold: "Dig the bed deep, keep the banks low." For
twenty-one centuries these instructions have been carried out. The stone
dikes are kept low to permit a judicious amount of flooding for
fertilization, and every year five to six feet of silt are removed from
the artificial channel of the Min. To this work the whole population of
the Chengtu plain contri