is likely that it continued being worked until the end of the 3rd century if not beyond. Hydraulic mining The Romans made extensive use of water carried by several aqueducts and leats, the longest of which is about from its source in a gorge of the river, to prospect for the gold veins hidden beneath the soil on the hillsides above the modern village of Pumsaint. Small streams on Mynydd Mallaen, the Annell and Gwenlais, were used initially to provide water for prospecting, and there are several large tanks for holding the water still visible above an isolated opencast pit carved in the side of the hill north of the main site. The larger aqueduct from the Cothi crosses this opencast, proving the opencast to be earlier. The water was stored in the tanks and then released suddenly, the wave of water sweeping away the soil to reveal the bedrock and any gold-bearing veins beneath. Pliny the Elder gives a dramatic account in his Naturalis historia of the method, possibly derived from his experiences in Spain. The method is known as hushing and survived in use until the 19th century in Britain, and into the 20th century in the goldfields of Africa. A not dissimilar method is used today in exploiting alluvial tin deposits, and is known as hydraulic mining. A smaller scale version of the same method is placer mining, and both may have been used to work alluvial placer deposits next to the river Cothi itself, judging by a large aqueduct which tapped the river a mile or so upstream, and enters the site at a low level compared with the other known aqueducts on the site. The water supply of the aqueducts was also used for washing crushed gold ore, and also possibly driving stamping mills for comminution of the ore (Lewis and Jones, 1969). One of the first aqueducts was built at a high level on the east slope of Allt Cwmhenog and tapped a small stream about away. There is a large tank at its end, where it sweeps around the brow of the hill onto the west side of the ridge. A gold vein must have been discovered here, because there is a large opencast below the tank. Yet the larger and longer aqueduct (with a gradient of 1 in 800) taps the River Cothi about to the north-east and traverses the same opencast,