cities and laid the foundations for the
nuclei of these civilizations.

Temples, tombs and other public constructs provided the centers around
which Egyptian civilization was built. The stone, wood and other raw
materials used in the building of these unique examples of human
handiwork were floated up and down the Nile from their sources of
origin. Annual Nile floods provided silt deposits necessary to fertilize
farms and gardens. Nile water, impounded during floods, irrigated the
land during the long dry seasons. Banked by deserts, the Nile was a
ribbon of fertility running through a largely uninhabited wilderness.
The upper reaches of the Nile lay in the mountains of Central Africa.
The Nile delta, built up through ages by silt deposits, provided a
meeting place where African, European and Asian traders could exchange
their wares and lay the foundations for the civilization of lower Egypt.
The Nile also provided the means of communication which connected Lower
Egypt with Upper Egypt and led, finally, to the unification of the two
areas in a long enduring and prestigious Egyptian civilization. Once
again geography was laying down the guide lines within which
civilizations have been built up and liquidated.

Thus far we have noted the role of physiographic factors that have led
to building the nuclei of empires and civilizations. They have been
parallelled by social factors as men took advantage of natural
opportunities to concentrate, feed and house ever larger human
aggregates.

Empires and civilizations have been built up by comparatively large
numbers of human beings concentrated in relatively small spaces.
Wandering food gatherers and herdsmen ranged widely in search of game
and grass. Cultivators settled in villages from which they could work
the land. If crops were scanty, population was sparse. Only abundant
crops, dependable, season after season, provided the basis for large
settled populations.

Large, settled populations, adequately supplied with the essentials of
life, enabled human beings to organize social centers in which a
comparatively few people, tending their animals and working the land,
could release a comparatively large part of the population to devote its
time and energy to trade and commerce, to industry and transport, to the
arts and sciences and to the organization, direction and administration
of large scale enterprises such as government, the military,
construction and the mobilization