Rudimentary incendiary grenades appeared in the Eastern Roman (Byzantine) Empire, not long after the reign of Leo III (717–741).[4] Byzantine soldiers learned that Greek fire, a Byzantine invention of the previous century, could not only be thrown by flamethrowers at the enemy but also in stone and ceramic jars.[4] Later, glass containers were employed. The use of Greek fire spread to Muslim armies in the Near East, from where it reached China by the 10th century.[4]
The shells (pào) are made of cast iron, as large as a bowl and shaped like a ball. Inside they contain half a pound of 'divine fire' (shén huǒ, gunpowder). They are sent flying towards the enemy camp from an eruptor (mu pào), and when they get there a sound like a thunder-clap is heard, and flashes of light appear. If ten of these shells are fired successfully into the enemy camp, the whole place will be set ablaze..