The Chinese used gunpowder to make fireworks and for signal flares. Gunpowder was also thought to have uses in medicine and in alchemy (the "science" of trying to change non-precious elements into gold). Soon after its invention, the Chinese used gunpowder for weapons (which they called fire arrows). Fire rockets were made by filling capped bamboo tubes with gunpowder and iron bits (shrapnel). These lethal weapons were attached to an arrow, lit, and shot from a bow. These were the first solid-fuel rockets. The Chinese used them to fight the invading Mongol hordes.