Byzantium kept Greek Fire secret by splitting the recipe

In 672 CE, with Arab fleets besieging Constantinople, a Christian refugee engineer named Kallinikos, fleeing Muslim-held Syria, gave the Byzantine navy a liquid incendiary weapon projected from ship-mounted siphons that reportedly kept burning even on water. It helped break the siege and became the empire's signature naval weapon for centuries. No patent system existed to protect an invention like this in the seventh century; the only real defense against a rival power copying it was making sure the knowledge never left Byzantine hands.

The obvious way to get the most out of a war-winning weapon is to scale it: train arsenal workers across the empire's shipyards, document the process so it survives any one craftsman's death or capture, and equip every fleet with local production. Each of those moves would also have multiplied the number of people who could defect, be captured, or simply talk, and rival powers from the Umayyad Caliphate onward wanted the formula badly enough to try.

Compartmentalized the recipe so no one held more than one step, and kept it in a narrow line, making capture or betrayal reveal only a fragment, never the whole.

No single person held the full recipe, so capture or defection revealed only a fragment.

Rival powers never obtained a working version across five centuries of attempts.

Emperors treated the secret as more protected than regalia or princesses, ensuring strict policy.

The same secrecy eventually caused the recipe to be lost when the specialist line died out.

For unpatentable process advantages, weigh compartmentalizing knowledge against the risk of losing it to institutional forgetting.

Byzantine forces used Greek Fire in recorded engagements for roughly five centuries, from its first documented deployment around 678 CE to the Fourth Crusade's siege of Constantinople in 1203–1204, after which no confirmed use appears in the historical record. No rival power is known to have obtained a working version of the formula in that entire span, an extraordinary run for a state secret with no legal protection behind it.