OTHER CENTERS OF CIVILIZATION 
horseback, but used chariots. They also offered horses at 
their most solemn sacrifices. 
The original Aryan-speaking races who settled in north- 
western India in time became modified, partly through 
climatic selection and partly through mixture with the 
darker-skinned peoples they conquered. Yet there, as else- 
where, they succeeded in imposing their language upon 
their subjects. As a result, over nearly the whole vast 
region of northern India today, in sharp contrast to most 
of the south, Aryan languages are spoken, although the 
people remain almost wholly of pre-Aryan blood. 
Thus sprang up, in the valleys of the Indus and the 
Ganges, the type of civilization which grew in time to be 
distinctively Indian. Great cities arose, built for the most 
part of wood and defended by massive wooden stockades. 
Tame elephants came to be employed largely in war. The 
chariot, just as in other lands, went gradually out of use 
with the development of cavalry. Iron appears to have 
been introduced about the eighth or ninth century B. c. 
and to have spread rapidly. 
What became of the earlier type of writing in use in the 
ancient Indus Valley culture remains unknown, but an- 
other form seems to have been brought in from western 
Asia by traders somewhere around 500 or 600 B. c., and to 
have been gradually adapted to the writing of Sanskrit 
and other Aryan tongues. 
Meanwhile an active development of civilized life had 
been going on in western Asia. Great monarchies had 
arisen, accompanied by an intense activity of war and 
trade, some of whose influences we can trace in regions far 
removed from their source. Finally on the ruins of the 
earlier kingdoms, embracing all their former territories 
and much more besides, arose the mighty Persian Empire, 
extending from southeastern Europe and Egypt on the 
one hand to the confines of India and central Asia on 
the other. The organizer of this vast power, Darius the 
Great, invaded and annexed the Punjab region of north- 
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