Both the Egyptian and the Aztec economies relied heavily on barter. Why is this so? Well, the primary point of this is that the Aztecs believed gold to be a myth, hence they did not even have any. As for obsidian, both economies used this but more so for rituals and ceremonial purposes. Chinampas were islands initially credited to the Aztecs. Because both economies required these things for their prosperity, trading was a heavily relied on factor. Barter is a synonym for trades, and would therefore be the answer. If you need to better understand, let me know and I will gladly assist you.