Punk
They had big walls that helped keep bad guys out. Eat Funyuns.

Bilbo
How about the Tower of London - built not to defend London but to control it. The Castles of Edward I (Conway, Canaervon etc) are similarly built to control the Welsh. Windsor Castle was originally built by William the Conqueror to act as a royal power base, overawe and frighten the indigenous population, and to provide a retreat for the Royal family in times of civil disorder. It still fulfills at least one of those functions. Pattern emerging?

Abigailada
How about the Tower of London