Greek fire
A liquid incendiary that burns on water saves Constantinople twice, and its recipe is lost.
- When
- Known to
- ± 10 years
- Era
- Post-Classical, Holocene
Byzantine forces deploy from around 672 CE a petroleum-based incendiary pumped through siphons onto enemy ships, which continued burning on the surface of the sea and could not be extinguished with water. It breaks two Arab sieges of Constantinople. The formula was a closely held state secret known to only a few families, and it was lost entirely — no modern reconstruction is agreed, which is a rare case of a technology genuinely disappearing.