London
During the 12th century, the institutions of central government, which had hitherto accompanied the royal English court as it moved around the country, grew in size and sophistication and became increasingly fixed in one place. In most cases this was Westminster, although the royal treasury, having been moved from Winchester, came to rest in the Tower. While the City of Westminster developed into a true capital in governmental terms, its distinct neighbour, the City of London, remained England's largest city and principal commercial centre, and it flourished under its own unique administration, the Corporation of London. In 1100, its population was around 18,000; by 1300 it had grown to nearly 100,000.

Q: What was the administration which governed the City of London called?
the Corporation of London