In Roman Britain, the Romans were exploiting all major coalfields (save those of North and South Staffordshire) by the late 2nd century AD. While much of its use remained local, a lively trade developed along the North Sea coast supplying coal to Yorkshire and London. This also extended to the continental Rhineland, where bituminous coal was already used for the smelting of iron ore. It was used in hypocausts to heat public baths, the baths in military forts, and the villas of wealthy individuals. Excavation has revealed coal stores at many forts along Hadrian's Wall as well as the remains of a smelting industry at forts such as Longovicium nearby.