Apparently llama dung made such good fertiliser that the Incas were able to cultivate maize which was easier to store than their traditional quinoa. This in turn freed up labour for road-building or constructing Inca trails. Thus maize was an essential ingredient in the expansion of the Inca Empire.
So when you visit Machu Picchu, trek the Inca Trail and visit the other Inca sites in the Sacred Valley or Cusco you now know how it came about!
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