eli5: Why were some ancient cities like Palmyra and Machu Picchu left to ruin and fall apart over hundreds of years instead of being repopulated?

Question

eli5: Why were some ancient cities like Palmyra and Machu Picchu left to ruin and fall apart over hundreds of years instead of being repopulated?

In: 1677

Answer 1

Large ancient cities rely upon the local infrastructure and farmland to feed the city population, if you can’t grow enough food and transport it to the city, then the population of the city can’t be sustained and it will be abandoned.