How did the kings of ghana become wealthy

Between the 9th and 11th centuries C.E., the kingdom of Ghana was so rich that its dogs wore golden collars, and its horses, which were adorned with silken rope halters, slept on plush carpets. Based on animal luxuries alone, it is no wonder that foreigners touted Ghana's kings as the richest men in the world. Gradually, Ghana grew very rich, due in large part to the trans- Saharan trade. The ghana required traders to give him a percentage of the products they were trading. If a trader was trading in gold, he was required to pay the ghana part of his gold. The ghana also placed a tax on the local goldmines.

i think it is a system for harvesting crops more easily

martin luther believed that selling indulgences was wrong and gave people a license to sin. the roman catholic church used the practice of indulgences to raise money for major building projects.