At Dolaucothi, a similar discovery was made in 1935 during mining operations, and it included part of a reverse overshot water-wheel which is now in the National Museum of Wales. It was found with burnt timbers, suggesting that fire-setting was used to help break up the hard quartz in which the gold was trapped. A similar but larger wheel was rediscovered during mine operations at Rio Tinto in Spain, and is now in the British Museum, where it is displayed prominently in the Roman gallery. The Spanish example included a sequence of no fewer than 16 reverse overshot water-wheels, each pair of wheels feeding water to the next set in the sequence. Each wheel would have been worked like a treadwheel, from the side rather than at the top, but it would have been a hard and lonely activity for the miners working these wheels lifting water from the mine bottom. Since the fragment of a reverse overshot water-wheel was found 160 feet below any known adit or stope, it must have been part of a similar sequence at Dolaucothi to that in Spain. Gold mining was sophisticated and technologically advanced at Dolaucothi, suggesting that the Roman army itself pioneered exploitation at the site. The construction of such dewatering machines is described by the Roman engineer Vitruvius writing in 25 BC, and their use for irrigation and lifting water in thermae was widespread.