Just southeast of Central Park, a group of men and women dressed in Colonial costume were headed north for a parade up Madison Avenue. Another group milled around a statue of Atlas, straining to hold the world on its massive shoulders.

A city is archeology laid bare. While it lives, the artifacts of the city spread outward rather than downward (though down too, of course – drilled deep into bedrock as metro lines and foundations of skyscrapers; and up as far as engineering will allow) – but a living city accrues in horizontal strata until all its space is filled and its growth is then redirected as a series of replacements. Buildings like microorganisms in a Petri dish, spreading from the points of greatest nutrient concentration into the surrounding lowlands.

Near Battery Park, where the city’s age is most visible in its brick streets and narrow, bending roads, I saw a sign for the Fraunces Tavern, the spelling itself an artifact. I recalled a story told about Benjamin Franklin: when the Constitutional Convention ended, a woman stopped him on the street and asked him what they had accomplished. He is said to have replied, “A republic, ma’am, if you can keep it.” I imagine New York as it stood in Colonial times, a lush green island dotted by brick and masonry settlements, livestock meandering on farms, and thickets of virgin wood still rattling with cricket-song beside the mud tracks that wove from village to village. For its time, a great and vital city, abutted right up against the tangled disorder of the wild. Franklin knew it: order is something borrowed, something hewn and crafted and needful of maintenance.

Further north the great hole in the ground left by the collapse of the Twin Towers is finally being filled. Two new towers are rising. Nearby a Colonial church is surrounded by prayers written on white paper, photographs, flowers. Inside the churchyard is a sculpture like the upended roots of a tree, rust-red and evocative of biological disorder. A surprising sight, inside a churchyard, and I imagine not much comfort to the prayer-writers outside its gates.

It occurred to me, as I traversed the city, that the wealth of a neighborhood rises as a function of its proximity to green leaves and water. The ornate Victorian co-ops and Art Deco skyscrapers, the immaculate glass and brushed-steel office towers up by 58th Street give way for a while to gritty tourist shops stuffed with cameras and cheap jewelry, only to rise again near Bryant Park, Gramercy Park, Washington Square Park, waves of money undulating over the city, clustering around the trees. Everyone wants to live near them.

We are of the wild, we humans. We were created by it. These things called cities arose at the very moment it occurred to some Fertile Crescent gleaner that plants grew from seeds and there might be an efficiency in placing the seeds where we would like them to grow. And with that we were off and running, unwittingly discovering the intense network effects of a settled, urban population.

We still grapple with those network effects. Because a city is formed of complex systems, and subject to sensitive dependence on initial conditions. Cities are organisms and we are the cells. Which cell controls the body? Which bird controls the flock? We created them, these behemoths, but they have a life beyond us. We fall off one by one and are replaced by new generations, but the cities lumber on. Our wild selves, hungry for safety and comfort from the elements, traded one kind of uncertainty for another. For we don’t know, no one knows, how far these creations will carry us, where they will bring us, and whether they will endure. We thought we were remaking the world in our image. Instead, we were making something new.