Emergent cities
Steven Johnson writes in Emergence how a series of events and innovations during the Middle Ages combined, causing larger towns to form. “First, the heavy wheeled plow, which tapped the muscular energy of domesticated animals, arrived with the German invaders, then swept through the river valleys north of the Loire; at roughly the same time, European farmers adopted triennial field rotation, which increased land productivity by at least a third.”
This meant that it became possible for larger towns to form, since the soil could feed larger population densities. Before, people needed to live more far apart. However, Johnson writes that in A.D. 100, there were several large towns, like for instance Rome. I wonder how this was possible. As I understand from his book, wars and invasions caused the cities and towns to “dissolve” and Europe being transformed to “a scattered, unstable mix of hamlets and migrants, with the largest towns holding no more than a thousand inhabitants” and that this remained the case for five hundred years.