New York

I stood on the 45th floor looking out over Central Park and experienced a moment of vertigo, more existential than physical. It occurred to me what an astonishing monument to impermanence the city really is. It is a city that is dependent entirely on its outside support network. Every element must work to near perfection. If any element fails, the city would die in a matter of days. It's like one of those Renaissance aristocrats who displays his power by engaging in no physical activity, awesomely powerful in society, but defenseless in person. New York has rendered itself nearly helpless as a symbol of its immense power - it alone can command the kind of support it takes to keep eight million people alive on a low-lying series of islands and peninsulas. Perhaps this is why New Yorkers are so edgy about crises, from power outages to terrorism - on some level, they know that if that intricate support network were to fail, even partly, their lives would not only become impossible, but unimaginable.

Humans like, I think, to imagine that the places they build are as permanent and solid as the mountains. But the Manhattan schist that pokes out of Central Park and the towering bluffs along the Hudson mock that. Humans can move flatten those mounds of rock, but only at enormous cost and effort. One could fly a fleet of aircraft into those bluffs along the river and barely make a mark.

As I looked out along the northward spread of Manhattan, I became suddenly aware how little stood between my feet and the ground 500 feet below.