When Monty Python referred to the Holy Hand Grenade of Antioch they were closer to the truth than they knew, although the wielder was on the other side. A ceramic vessel found in Jerusalem and likely to date from the 12th century contains chemical residues consistent with it once containing explosives. It is likely the vessel represented a sort of medieval hand grenade, probably thrown by Saladin's forces during the Siege of Jerusalem in 1187 CE. The finding supports claims hand-held explosive devices were used during the Crusades, but this recipe never reached beyond the Middle East and North Africa,
Spherical and conical ceramic vessels dating from the ninth to the 15th century are found widely across the Middle East, but their uses are debated. Speculation has included that they held mercury for mining and its medicinal purposes (if it didn't drive you mad), beer, and scented oils.
Dr Carney Matheson of Griffith University has analyzed residues inside four of these vessels, all found in Jerusalem's Armenian Gardens in a layer dating to the 11th and 12th centuries. In PLOS ONE Matheson, ceramicist Rob Mason, and co-authors report each has a different chemical make up, supporting the idea these vessels had diverse uses.
One of the four, dubbed sherd 737, is easily the most significant, containing a flammable mixture that was probably used as an explosive. Rather than being an import from China, where gunpowder had been used since at least the ninth century, it seems this explosive was of local manufacture, and possibly invention.
Sherd 737 contains traces of sulfur, mercury, magnesium and nitrates suggestive of a sophisticated explosive device very different from the black powder soon to arrive from China. The magnesium, for example, may well have come from the Dead Sea, where it was extracted at the time.
“These vessels have been reported during the time of the Crusades as grenades thrown against Crusader strongholds producing loud noises and bright flashes of light,” Matheson said in a statement. “Some researchers had proposed the vessels were used as grenades and held black powder, an explosive invented in ancient China and known to have been introduced into the Middle East and Europe by the 13th century. It has been proposed that black powder may have been introduced to the Middle East earlier, as early as these vessels from the 9th-11th century.”
Matheson told IFLScience Arabic texts from the time refer to recipes that appear to be for explosives, but they have proved hard to replicate. “These were secret weapons and they didn't necessarily want to tell everyone exactly how to make them,” he said. Modern translations may not be completely reliable and each recipe differs. Some call for dolphin fat, which Matheson added could be a cover to make the manufacture sound more difficult than it really was when sheep fat would do just as well.
Based on what he found on sherd 737 Matheson told IFLScience: “If you mixed Dead Sea salts and urine [with plant and animal fats] you'd get something like what we found.”
The use of burning arrows to start fires in enemies' fortresses probably dates back thousands of years, and sulfur has been added since at least 429 BCE. However, Matheson thinks there was more to these ceramics than fire starters. Some of them were sealed with resin. Combined with the strength of the ceramic – fired at temperatures of up to 1,300ºC (2,400ºF), far above the temperatures used for most pottery – this made them exceptionally strong. Matheson told IFLScience, “We think the pressure could build up inside until it could explode in fragments,” magnifying the effect.