Two thousand years before the first vending machine patent, a scholar in Roman-era Alexandria dropped a coin into a slot and watched holy water pour into his hands. That machine — and the automated temple doors, self-driving cart, programmable theater, and proto-steam engine built by the same man — belonged to Heron of Alexandria, a figure historians call the greatest experimentalist of antiquity. Working at the Mouseion, the institution that housed the legendary Library of Alexandria, Heron operated at the crossroads of Greek mathematics, Egyptian ingenuity, and Roman engineering culture. His personal life is almost entirely unknown — we cannot pin his birth or death to a specific year, and even his ethnicity is a matter of informed speculation in a city defined by its cosmopolitan mixing of Greek and Egyptian populations.

What survives ar ...