Two other points that might be worth further exploration: * There was an article on Hacker News recently about the historical cost of clothing, how it used to

Two other points that might be worth further exploration: * There was an article on Hacker News recently about the historical cost of clothing, how it used to cost thousands of modern-equivalent dollars for a shirt. Thus why people wore clothing until it was rags. The cost of clothing and all such goods came down dramatically due to peoples' specialization as spinners, weavers, sewers, tailors, etc. Now clothing is cheap and plentiful. [Update: found it: https://news.ycombinator.com/item?id=8940950 https://news.ycombinator.com/item?id=8940950 ] * There was another HN thread discussing the fall of the Roman empire and the "dark ages". A commentator who seemed to be a historian reinforced the idea that yes, there really was a dark ages. The fall of the empire shut down trade, which led to a marked decline in the pottery available in Britain. Previously they had been able to import plentiful, high quality pottery from elsewhere. With the fall of the empire and the collapse of trade, they began to make it themselves, and were terrible at it. Even the kings of the era had worse pottery than the common person centuries earlier. (This is more about trade than about cities, but the effectiveness of trade increases with density.) [Update: not the HN comment I was looking for, but similar information about pottery: http://www.thehistoryblog.com/archives/1391 http://www.thehistoryblog.com/archives/1391 ] The power of specialization and trade