The invention of gunpowder revolutionized the way battles were fought. Gunpowder, which is also known as black powder, is made by mixing sulfur, potassium nitrate (saltpeter), and charcoal. Although, most historians believe that it was the Chinese who invented gunpowder, some contend that the discovery of the explosive could have been made elsewhere too, specially in Europe and the Arab world. Nevertheless, all agree that the Chinese did guard their discovery from the rest of the world with quite some zeal, till their secret finally leaked out sometime between the 11th and 12th century. It was in ancient China during the 9th century that it was realized, that gunpowder could be used in weapons. Nevertheless, it is believed that the alchemists had already stumbled upon the components of gunpowder and were aware of their combustible properties long before the Chinese used it. There is conclusive evidence that the Chinese alchemists knew about saltpeter as early as mid 1st century. Saltpeter and sulfur were largely used in traditional Chinese medicine. The earliest mention of gunpowder dates to 142 AD, during the rule of the Han dynasty. A Chinese alchemist named Wei Boyang was the first to have provided a written account of gunpowder. He mentions of a mixture of three powders that would 'fly and dance violently' when ignited. No more information about this powder is available in his writings. However, it is assumed that it is gunpowder that he was talking about, as no other explosive made from three powders had been known to the world at that time. But there are some who contend that Wei Boyang was probably a Taoist who was looking for some magic potion that would grant one immortality, which was what a lot of Chinese alchemists were working on in those days! The evolution of gunpowder for use in weapons was gradual. A text written in 300 AD by a Chinese scholar by the name Ge Hong makes clear mention of gunpowder and more importantly, its explosive nature. He belonged to the times of the Chin dynasty. However, in his writings he also mentioned that the alchemists of those times were unable to rein in the combustion of the explosive mixture, something that some of the researchers had to pay for with their lives. It was only in the 7th century AD during the rule of the Tang dynasty, that the explosive nature of gunpowder could be regulated and put to use. Some records about discovery of gunpowder indicate that the Tang dynasty used the mixture in ancient Chinese fireworks. However, since the end of the Tang dynasty, by the early 10th century, the Chinese made crude rifles by filling hollow bamboo sticks with gunpowder. They packed one end with gunpowder and put a metal ball from the other. They ignited the gunpowder, which made it explode and propel the metal ball at a speed that could exert considerable damage to an enemy soldier. Rifles and cannons made from iron had not been invented till the 12th century. What transpired in between is a little sketchy. Some argue that the Chinese were already using gunpowder during 904-906 in making incendiary projectiles called fei-ho (flying fire). However, some debunk this claim. They say that it was first used by Chinese in battles in 919 AD to ignite another incendiary called the 'Greek fire'. A mid 10th century Chinese silk banner shows them using a fire lance - the precursor of the gun that used gunpowder. The earliest recipe for gunpowder to be used in warfare was found in the Chinese military compendium that was written in 1044 during the rule of the Northern Song Dynasty. By the 12th century the Chinese had started using gunpowder rifles and canons made from iron under the Song Dynasty. Spread of the Knowledge of Gunpowder The Chinese tried hard to keep the knowledge of gunpowder a secret from the rest of the world. As early as the 11th century, the Song dynasty prohibited its people from trading sulfur or saltpeter with any foreigner. But while the Song dynasty was perfecting its firearms, its secret of gunpowder leaked out to the Islamic world and the Roman Empire. It is largely believed that the Islamic world acquired knowledge of the explosive mixture sometime between 1240 and 1280. From here, recipes of gunpowder spread throughout the world. It is generally believed that gunpowder technology was brought to India in the mid 12th century by the Mongols, who had conquered both India and China. However, others contend that it reached India only about a hundred years later. Knowledge of gunpowder soon spread to Europe, probably through the Third Crusade or through the Silk Route. Roger Bacon of England is one of the first Europeans who made a mention of gunpowder in his writings. Gunpowder was used for the first time in Europe in the Battle of Crecy which was fought in 1346. Some historians credit the invention of gunpowder to the Arabs, Roger Bacon, and also to Berthold Schwarz, a Franciscan monk from Germany.