She is the personification and patron deity of the British Isles. No sooner did the Romans invade Britain than they had to invent a goddess of the place to apologize to. The locals probably found this very strange behavior.
BRITANNIA found a new lease of life during Victorian times when she became a symbol of stiff-upper-lipped Empire-building. Somehow the Victorians never managed to invade Rome so she is still waiting for a chance to get her own back.