The terrace on the east side of the street called Norton Folgate is one of the grimmest in central London: a closed department store, a defunct catering company, the headquarters of something once called the British Atomic Nuclear Group. It was shuttered even before austerity struck Britain, and it is dirty and shuttered now.

But the west side of the street is dazzling: The sheer, clear glass of the world’s mightiest financial center towers above you. It is as if you are staring not across a two-lane highway, but into a different dimension.

That is the City of London. The City is not to be confused with London, although they share a name. The City is much smaller and far older. London is the capital of England, but the City, the ancient heart of Greater London, is the capital of capital—and when the offices glow with light on a dark March evening, it looks the part.

Some 350,000 people work in this square mile of real estate, but the City is not just a money machine. It has the oldest representative body of local government in the world, and is a unique combination of private company and public authority. This hybrid entity, called “the Corporation,” is vastly wealthy, and has used that wealth—and its attendant connections—to charm friends and buy off enemies for centuries. Though its electoral freedoms long predate those of the rest of Britain, the City is also swathed in the kinds of mystery and ritual rarely seen outside the Vatican.

But north of Norton Folgate is a warning for anyone about to enter these canyons of glass and steel. There on a brick gable beyond the City’s limits is some white graffiti. Written out in block letters, positioned to be legible to the office workers, it says: “We will ask nothing, we will demand nothing, we will take. Occupy.”