Gunpowder was invented in China during the late Tang dynasty (9th century). Knowledge of gunpowder spread - possibly because of the Mongol conquests of the 13th century; possibly along the Silk Road. A written formula for it appeared in the 1267 Opus Majus prepared for the Pope by Roger Bacon in England. English cannon saw its first use in the Hundred Years War (1337-1453). Masters of Ordinance were created in 1414. Early guns were ‘guns of position’, used in defence of castles, but not easily moved until the middle of the 15th century as wheels and carriages improved. King Henry VII (1509-1547) appointed a Master Gunner at the Tower of London and Master Gunners were appointees at castles where they were responsible for maintaining the armament and training the gunners (who were civilians). In 1602 the Office of Master General of Ordinance was created to organise trains of artillery, allot guns and master gunners, hire horses and drivers and appoint army officers to control them. In action gunners were assisted by soldiers who could be made available. As gunnery became more technical the new ranks of firemaster, fireworker and bombardier were introduced. Trains of artillery became very large and the organisation of these trains became so complex that, after the failure of a train to arrive on time in 1715, it was decided to raise two permanent companies of artillery on a military basis to be stationed at Woolwich, East London. Thus, on 26th May 1716, the Royal Artillery was born.