When I was twelve, I was fortunate enough to hike part of Hadrian’s Wall in Northern England. Of all of the astounding qualities of this Roman fortification, I can still recall the sewage system constructed almost two millennia ago in those barren hills. These primitive sewers enabled the Romans to build densely populated forts, which helped extend their far-reaching empire.

I’m thrilled that MacKenzie has chosen to highlight such an unsexy technology. Sewers are gross! Filled with excrement and stinking to high heaven, we envision dank tunnels teeming with rats. Who could like sewers? But! Sewers make our modern existence possible. Buried under our cities and towns are vast, complex, and hugely important technological marvels that transport and process quantities of waste that are difficult to fathom.

And yet! While the Romans implemented sewers in the farthest reaches of their empire two thousand years ago and modern cities have implemented enormously complex sewer networks, in many parts of the world adequate sewage systems are still sorely needed. Contaminated drinking water kills millions of people every year and sickens many more.

Around the globe, adequate sewage systems have the potential to save so many lives. Even though sewage technology is ancient, engineers, entrepreneurs, politicians, and other innovators are presented with an enormous opportunity to find improvements that can bring about global change.