Their dung was harvested in Persia, and it still is today. This could be done in cities. https://news.ycombinator.com/item?id=31885525 https://news.ycombinato

Their dung was harvested in Persia, and it still is today. This could be done in cities. https://news.ycombinator.com/item?id=31885525 https://news.ycombinator.com/item?id=31885525