iron plough-shares became more common. A fallow system was introduced so
that cultivation became more intensive. Manuring of fields was already
known in Shang time. It seems that the consumption of meat decreased
from this period on: less mutton and beef were eaten. Pig and dog
became the main sources of meat, and higher consumption of beans made up
for the loss of proteins. All this indicates a strong population
increase. We have no statistics for this period, but by 400 B.C. it is
conceivable that the population under the control of the various
individual states comprised something around twenty-five millions. The
eastern plains emerge more and more as centres of production.

The increased use of metal and the invention of coins greatly stimulated
trade. Iron which now became quite common, was produced mainly in
Shansi, other metals in South China. But what were the traders to do
with their profits? Even later in China, and almost down to recent
times, it was never possible to hoard large quantities of money.
Normally the money was of copper, and a considerable capital in the form
of copper coin took up a good deal of room and was not easy to conceal.
If anyone had much money, everyone in his village knew it. No one dared
to hoard to any extent for fear of attracting bandits and creating
lasting insecurity. On the other hand the merchants wanted to attain the
standard of living which the nobles, the landowners, used to have. Thus
they began to invest their money in land. This was all the easier for
them since it often happened that one of the lesser nobles or a peasant
fell deeply into debt to a merchant and found himself compelled to give
up his land in payment of the debt.

Soon the merchants took over another function. So long as there had been
many small feudal states, and the feudal lords had created lesser lords
with small fiefs, it had been a simple matter for the taxes to be