"The secret of the Inca's great wealth may have been their unusual tax system. Instead of paying taxes in money, every Incan was required to provide labor to the state. In exchange for this labor, they were given the necessities of life.
Of course, not everybody had to pay labor tax. Nobles and their courts were exempt, as were other prominent members of Incan society. In another quirk of the Incan economy, nobles who died could still own property and their families or estate managers could continue to amass wealth for the dead nobles. Indeed, the temple at Pachacamac was basically a well-managed estate that 'belonged' to a dead Incan noble. It's as if the Inca managed to invent the idea of corporations-as-people despite having almost no market economy whatsoever.
One of the outstanding questions for scientists and historians who study the Incas is why this wealthy, sophisticated culture developed scientifically and culturally without ever inventing markets. One possibility is that life was so difficult to sustain in their environment that all their innovations revolved around agriculture rather than economics. In other words, the Inca Empire was optimized to prevent starvation rather than to foster trade."
I would suspect that there could be archeologists who would dispute this interpretation of Incan economics. Nevertheless, it is interesting to think that an empire could function with no money. Perhaps we have more options than we know.