e they cultivate lands reclaimed
from the sea; or as colonists in the Vistula lowlands, whither Prussia
imported them to do their ancestral task, just as the English employed
their Dutch prisoners after the wars with Holland in the seventeenth
century to dike and drain the fens of Cambridgeshire and Lincolnshire.
Moreover, the commercial talent of the Dutch, trained by their
advantageous situation on the North Sea about the Rhine mouths, guided
their early traders to similar locations elsewhere, like the Hudson and
Delaware Rivers, or planted them on islands either furnishing or
commanding extensive trade, such as Ceylon, Mauritius, the East Indies,
or the Dutch holdings in the Antilles.

Much farther down in the cultural scale we find the fisher tribes of
Central Africa extending their villages from point to point along the
equatorial streams, and the river Indians of South America gradually
spreading from headwaters to estuary, and thence to the related
environment of the coast. The Tupis, essentially a water race, have left
traces of their occupation only where river or coast enabled them to
live by their inherited aptitudes.[205] The distribution of the ancient
mounds in North America shows their builders to have sought with few
exceptions protected sites near alluvial lowlands, commanding rich soil
for cultivation and the fish supply from the nearby river. Mountaineer
folk often move from one upland district to another, as did the Lombards
of Alpine Pannonia in their conquest of Lombardy and Apennine Italy,
where all their four duchies were restricted to the highlands of the
peninsula.[206] The conquests of the ancient Incas and the spread of
their race covered one Andean valley after another for a stretch of one
thousand five hundred miles, wherever climatic and physical conditions
were favorable to their irrigated tillage and highland herds of llamas.
They found it easier to climb pass after pass and mount to ever higher
altitudes, rather than descend to the suffocating coasts where neither
man nor beast could long survive, though they pushed the political
boundary finally to the seaboard. [Map page 101.]

[Sidenote: Movement to better geographic conditions.]

The search for better land, milder climate, and easier conditions of
living starts many a movement of peoples which, in view of their
purpose, necessarily leads them into an environment sharply contrasted
to their original habitat. Such has been the radia