Frontinus, the Roman senator appointed curator aquarum — superintendent of waters — in 97 AD, opened his report on Rome’s water supply with a sentence that has been quoted many times since: compare, if you will, the idle pyramids, or the useless though famous works of the Greeks, with these many indispensable structures. The arrogance is characteristic, and the comparison is not entirely fair. But the underlying point is not wrong. Rome’s aqueduct system was among the most impressive engineering achievements of the ancient world, and it was, unlike the pyramids, entirely functional — designed to do something specific, doing it at scale, and doing it for centuries.