For thousands of years, trade was based on the barter system-the exchanging of goods or services As nations became powerfully wealthy, new ideas took
shape evolving into an economy based on gold or money. This new economy was
known as:

currency trade

Explanation:

this is because currency is a form of buying goods while barter trade is a form of exchanging goods

what the first or next guy says

the crusaders are identified in the painting;

c. by the red crosses on their backs