The Aztecs were unable to grow cacao themselves, as their home in the Mexican highlands was unsuitable for it, so chocolate was a luxury imported into the empire. Those who lived in areas ruled by the Aztecs were required to offer cacao seeds in payment of the tax they deemed "tribute". Cocoa beans were often used as currency. For example, the Aztecs used a system in which one turkey cost 100 cacao beans and one fresh avocado was worth three beans.