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, so must be later in date.