How cities get their shape, and why the sun was never consulted

At the end of a henge street the sun looks like it has found the place it was always meant to sit. The road runs straight at it. The buildings hold it up between their walls. For a few minutes the whole city seems to be letting you in on a plan it had all along.

The sun is the old, simple half of that picture. It has been making the same slow trip along the horizon since long before there were streets or cities or people standing around with cameras, and it will keep making it long after. The street is the odd thing in the scene. It is a line somebody decided to scratch across the ground, almost always for a reason that had to do with money or ownership or getting an army from one gate to another. Other people came along and paved it, built up its sides, gave it a name, and learned to live their whole lives by it. The decision that set its direction stayed inside the city, sometimes for hundreds of years, quietly holding its angle while everything around it changed.

A henge photograph is the short moment when those two histories cross. One of them belongs to the solar system. The other one may well have started in a surveyor's back office.

Most tellings of the henge spend all their time on the sun and get rid of the street in two words, "the grid," as though that settled it. But the grid is not just the backdrop the sun performs against. Its angle is what fixes the date. Where it came from is the reason the street is there at all. And the fact that it was drawn without a single thought for the sky is the reason the alignment is a coincidence and not a monument.

The urban historian Spiro Kostof spent two long books, The City Shaped and The City Assembled, arguing that the plan of a city is never purely practical and never quite an accident. It holds old decisions about who owned what, who was in charge, how people and armies moved, what needed defending, and what was meant to be looked at. A henge street is one of those old decisions, caught for a few minutes in the geometry of a different system entirely.

Before the sun comes into it, it helps to look at the kinds of line a city can end up with.

Kostof's three broad families of urban form: the grid; the organic or "diagram" city shaped by terrain and accumulated use; and the grand manner, whose avenues are directed toward monuments and distant views. Each gives its streets their bearings, long before the sun is considered.

The grid: a machine for selling land

The grid is one of the oldest planning ideas that anyone bothered to attach a name to. Kostof traces the attachment to Hippodamus of Miletus, in the fifth century BCE, though he is careful not to hand Hippodamus the geometry itself. Gridded colonial towns were already older than that, and they already cut their land into equal lots.

What later writers pinned on Hippodamus was a bigger idea. It was that a city could be thought out whole, in advance, as one finished arrangement, instead of being allowed to gather its shape slowly over generations. Aristotle gave him the credit for discovering "the art of planning cities," and Miletus became the model for what got called the modern Hippodamean fashion.

The grid lasted because it is useful in ways that have nothing much to do with beauty. It cuts the ground into rectangles that are easy to measure and write down and tax and buy and sell and build on. You can extend it without imagination and copy it without an argument. On paper each block looks like the one next to it.

Kostof quotes Lewis Mumford on nineteenth-century American planning:

"An office boy could figure out the number of square feet involved in a street opening or in a sale of land. With a T-square and a triangle the municipal engineer could, without training as either an architect or a sociologist, 'plan' a metropolis."

The grid in that description is not innocent geometry. It is a tool for turning land into things you can count.

The most photographed grid on earth was put down with that job spelled out about as plainly as it ever gets. The Commissioners' Plan of 1811 threw a single regular system across almost all of undeveloped Manhattan and produced something like two thousand blocks that could be chopped up and sold. The Commissioners defended how little public space they had left by explaining that, since "the price of land is so uncommonly great, it seemed proper to admit the principles of economy to greater influence."

Kostof's own gloss is blunter: "when there is the chance of making money from urban land, the claims of the public good will be set aside."

The plan did not invent the habit. Back in 1796 the surveyor Casimir Goerck had already cut a strip up the middle of the island into regular lots for auction. The Commissioners took that procedure and enlarged it until it was the future city. This is where Manhattanhenge really begins. Not with an astronomer, but with a piece of ground being measured and numbered and got ready to sell, and the sun nowhere in the room.

Why grids point where they point

Every grid still has to be turned to face some direction. Some of them are set close to the compass, one set of streets running north and south, the other east and west. The big American land survey pushed that arrangement across most of the country west of the old colonies, because a compass bearing and a surveyor's chain could carry the same rectangular logic over ground the government had not even mapped yet. Chicago came up inside that near-cardinal order. A lot of its downtown streets run almost dead east and west, so the setting sun comes down them around the equinoxes, when it reaches true west.

Other grids are tilted to fit a shoreline or a valley or a river or an older road or the edge of somebody's field. Manhattan's is turned about twenty-nine degrees off true east and west, and the reason is completely practical. The long avenues follow the run of the island, while the cross-streets take the short way from one river to the other. That one adjustment, made to sit the streets more comfortably on a long thin island, is what slid Manhattanhenge off the equinoxes and into late spring and midsummer. A convenience became, two centuries on, the date of a public sunset.

Turn the grid and the henge moves with it. A street running due east to west catches the setting sun near the equinoxes. Rotate the same street for the shape of an island, and the alignment appears elsewhere in the year.

Nothing in that first choice had to touch the sky. One system got fitted to the land and to the arithmetic of selling it. The other kept walking along the horizon the way it always had. Sooner or later the two of them ended up pointing the same way.

The organic city: shaped by everything except a plan

Plenty of cities never got a single governing angle at all. Kostof's second family is the organic city, or what he sometimes calls the diagram city. Its streets were not drawn all at once by anybody. They gathered around a hill or a market or a gate or a river crossing or an old wall or the edge of a field that vanished centuries ago. Le Corbusier waved such places off as the work of the Pack-Donkey's Way, the wandering track an animal takes to get around obstacles and up the easy slopes. Kostof is gentler with them. He points out that the apparently unplanned city is usually made of short straight runs, each one sensible for its own little patch of ground, joined by bends that keep a record of who owned what and where the hill was.

The result can look like a mess from above and still be perfectly clear on foot. A street bends because something once made it bend. For a henge, though, all of this is a problem. A curving street has no one bearing. Its direction changes from block to block. It gives the sun a lot of short openings and almost never the long straight corridor you need for the whole view to line up at once. That is why the named henge events turn up in gridded cities and along deliberate avenues and not in the older tangle around them. When an organic city does throw one up, it is usually on some later street that got driven straight through whatever was already standing.

The grand manner: aimed at something else

Some streets make no secret of their intention. They aim straight at a palace or an arch or a dome or a hilltop, at some monument set down on purpose to close off the far end of the view. Kostof calls this the grand manner, a whole language of straight avenues and radiating plans and monumental junctions and streets that end on something worth ending on. It belongs to Baroque Rome and to Versailles and to Haussmann's Paris and to Washington. Its streets were built to be read as compositions, and their size took both a concentrated kind of power and the means to knock down anything in the way.

Kostof ties the mature grand manner to the intellectual weather of the Copernican revolution. The same age that shoved the earth out of the middle of the universe was also working out new things about optics and perspective and ordered space, and in political life kings and states were busy installing themselves in the middle instead.

The likeness can fool you. A monumental avenue can look as though it might have been pointed at the sky precisely because it is so obviously pointed at something. Nearly always the something was down here on the ground. The Champs-Elysees, where Paris Henge shows up, is the clean example. Its line was worked up over centuries as a controlled view and finally capped by the Arc de Triomphe, and few streets on earth have been composed with more care for the thing at their far end. That thing was not the sunset. The alignment comes from the same gap you see in Manhattan. The avenue got its bearing from a plan that cared about ceremony and perspective and power, and the sun reached the same bearing later, on its own yearly round. The care was real. It was just aimed somewhere else.

Reading the old line

So a henge is picky about streets. It needs a corridor long enough and straight enough to hold one bearing all the way down, which usually means a grid, where the angle got chosen for survey and division, or a monumental axis, where it got chosen to steer the eye toward something built. The organic city tends to turn away before the alignment can finish arriving.

The street's origin stays visible right there in the event. Manhattan is carrying the arithmetic of a land sale. Chicago is carrying the cardinal order of a continent being surveyed. Paris is carrying the theater of a monumental view. Each city hands the same sunset a different frame, because each one arrived at its street line by a different road.

Knowing all this does not shrink the henge down into planning history. It gives the photograph its second subject. When the sun reaches the end of West 42nd Street, nothing secret is revealed about the Commissioners of 1811. They did not see it coming, and they did not intend it. What you are actually watching is how well their line has held, a piece of two-hundred-year-old land arithmetic still keeping its bearing while the sunset slides down it. For a few minutes the city and the sky share one number. Then they come apart again.

Sources

• Spiro Kostof, The City Shaped: Urban Patterns and Meanings Through History (Thames and Hudson, 1991), read directly from the full text for this piece. The Hippodamus material, the "office boy" quotation from Lewis Mumford, and the account of the grid as a real-estate instrument are from the book's chapter on the grid; the Commissioners' Plan of 1811 quotations ("the price of land is so uncommonly great," and Kostof's gloss that "when there is the chance of making money from urban land, the claims of the public good will be set aside") and the Casimir Goerck 1796 detail are from the same chapter's New York discussion. The grand-manner material, including the link to the Copernican sun-centered universe and the observation that the grand manner "is routinely associated with centralized power," is from the book's grand-manner chapter.
• The Le Corbusier "Pack-Donkey's Way" quotation is quoted by Kostof from Le Corbusier's 1924 Urbanisme; it is cited here as Kostof cites it, not from the original.
• Manhattan's roughly twenty-nine-degree grid rotation and its role in setting Manhattanhenge's dates, and Chicago's near-cardinal grid, are widely reported general record; the specific street bearings this series uses (New York, West 42nd Street; Chicago, West Madison Street) are from Streethenge's own catalog, computed by the same engine the site runs.