 There are some exceptions such as the Hillfort of Otzenhausen, a Celtic ringfort with a thickness of forty meters in some parts, but Celtic fort-building practices died out in the early medieval period.Andrade goes on to note that the walls of the "marketplace" of Chang'an were thicker than the walls of major European capitals.Aside from their immense size, Chinese walls were also structurally different from the ones built in medieval Europe.