What If the Library of Alexandria Never Burned?

By the year 1000, three cities — Alexandria, Baghdad, and a reluctant newcomer in Córdoba — maintained observatories that compared notes by letter, arguing over the same data across three languages and two religions, more often as rivals than collaborators, but reading each other's work all the same. A Córdoban physician cross-referencing Alexandria's surviving medical texts with his own clinical notes isolated the pattern of a disease later generations would call smallpox, and proposed — correctly, though no one could yet explain why — that prior infection granted future protection.

He did not have the tools to prove it. His paper sat, mostly ignored, in an archive for sixty years until a student copying it for a different purpose noticed the claim and ran her own trial on a reluctant village, inoculating twelve children with matter from a mild case, against the furious objections of the local priest.

Ten of the twelve survived the epidemic that swept through six months later. The other fifty children in the village did not. It was not kindness that made the method spread after that. It was arithmetic that any parent could do for themselves, and a network of libraries built, three centuries earlier, specifically so that an answer this important would never again have to wait for the right building not to catch fire.