In the 16th century, pigeon droppings were so valuable for making gunpowder that they were guarded by armed men.

Gunpowder, also known as black powder, consists of sulfur, charcoal, and saltpeter, with saltpeter making up about 75% of the mixture. During the 16th and 17th centuries, saltpeter was incredibly difficult to source naturally in Europe. It was primarily harvested from the nitrogen-rich 'petre-dirt' found in stables, cellars, and dovecotes where animal waste accumulated.The British Crown, particularly under King Charles I, granted 'saltpeter men' extraordinary legal powers to dig up the floors of private barns and dovecotes to retrieve this waste. Because England lacked large natural deposits of nitrates, these pigeon droppings were considered a critical national security asset. The process involved leaching the soil with water and wood ash to extract potassium nitrate crystals through evaporation.By the mid-1600s, the demand for gunpowder for the English Civil War and naval expansion made saltpeter more valuable than gold in some contexts. Armed guards were often stationed at large dovecotes to prevent 'nitre-poaching' by unauthorized collectors. This domestic production remained vital until the late 18th century, when the British East India Company began importing massive quantities of high-quality saltpeter from India, eventually making the 'saltpeter men' obsolete.