Economy
This is one of the most amazing elements to do with the Incas, they were the largest empire South America had ever had at the time, yet they had no form of currency! The incas paid taxes by doing services for the emporer, and in return he gave the people the neccesities they needed. Another way they could have a working economy without currency is they traded with each other. The incan people were very good at farming and were the first to plant potatos, but that's off subject, so if one family were farmers and another family were craftspeople, the farmers could trade the food they made for blankets, pots, or pan the the craftspeople made! This is the only thing they could do if they were able to have a well-working economy without money.