The outflow was channelled into sluice boxes, and the heavier gold collected on rough pavements. They also developed many deep mines, such as those for copper at Rio Tinto, where Victorian mining developments exposed the much earlier workings. Dewatering machines, such as Archimedean screws and reverse overshot water wheels, were found "in situ", one of which is on show at the British Museum. Another fragmentary example was recovered from the Roman gold mine at Dolaucothi in west Wales, and is preserved at the National Museum of Wales in Cardiff. The army were at the forefront of development of gold mines, since the metal was imperial property, and developed the Dolaucothi mines from the outset by establishing a fort there that was known as Luentinum. They had the expertise to build the infrastructure of aqueducts and reservoirs, as well as control production.