Two acres is the approximate area of a typical soccer field. The list above compares the outer circular walls of several castles, but if they are truly comparable or not, could be disputed. The Kremlin, for example, could be considered a district of the city rather than a mere fortification. Castles might be constantly or permanently inhabited so the strategic value and the fighting ability of its garrison remain uncertain.

Those Ottonian fortifications, where merchants were active, could also be considered early cities. Whether Werla fits this description is uncertain. Some late medieval cities, with an area comparable to the outer perimeter of Werla, had a population of about three thousand but Werla, with its single storeyed construction, could not have had more than one thousand inhabitants.