I’ve been thinking a lot about infrastructure lately. And about the arc of infrastructure, such as the damming of the Hetch Hetchy Valley in the High Sierra nearly a century ago. A full day away from San Francisco, it was out of sight and out of mind. Its roaring aqueducts drove across the hot Central Valley of California, slipped under the bay and wove their way into the kitchen taps of fog-bound San Francisco, delivering crystal clear snowmelt. It was like importing manna from heaven with no middle man to gum up the works.

Now a century has passed, and all of California has become easily accessible and developed. “Out of sight” has given way to “in plain view,” and the city not only still needs water, so does the great central valley. Water up and down the state has writ large the history of California, bringing it to where it is today, the fifth largest economy in the world – all by itself.

You’d never get away with it today, this damming of a wondrous natural resource. But it is also true that California would never have begun its ascendancy without it.

The arc of infrastructure is also the arc of technology, and it begins with a projected need or perhaps an overwhelming, behind-the-eight-ball need, gets implemented, and eventually, at some point, becomes beside the point.

Needs change. Technologies crumble. Or both.

Mix the arc of technology with the reality of economics, and you will see that it is rich communities which build infrastructure in the first place, and eventually they find themselves on the downside of the arc of that technology in its waning days. The rich had better be richer still, because they’ve got to prop up the aging infrastructure, while building up the next.

And herein lies the point of opportunity for the previously poor and now reasonably well-heeled. Not burdened by a declining infrastructure, the newest technology can be brought into play. Their fortunes may rise, while the previously powerful may falter, burdened by the legacy of civic visionaries long gone.

This is not a new scenario, nor is it an uncommon one.

A few centuries after the fall of Rome, the city had dwindled to tens of thousands of people, the equivalent of a small suburban American town. What the mighty Roman aqueducts had been used for was anybody’s guess, a prominent one being the transport of olive oil. But there, among the ruins of a monumental infrastructure, Rome continued and lived on to thrive another day, or perhaps more accurately, in another century, when the bill for its ancient technology had been paid in full.

Today’s less economically viable countries have satellite dishes to catch the broadcast waves, satellite phones to enable their calls, and little or no 50-year-old technology to add to their challenges.

No doubt, a few of their citizenry will see, with a little smart investment in new technology, that there is an opportunity in the next emergent wave of global economics. And the cycle will begin again.

The fortunes of the citizens will rise. And the proverbial “City Fathers” and entrepreneurs behind it all will be gone before the arc of the latest technology plays out.

So keep an eye on these movers and shakers, who think it all such a good idea in the first place. They are members of an anonymous brotherhood with those earlier visionaries who thought to dam the Hetch Hetchy and build the aqueducts of Rome, neither realizing nor grasping the totality of what they create.

I'm Moira Gunn. This is Five Minutes.