when streams began to dry up, although Lamberhurst Furnace driven by the River Teise ran continuously for more than three years in the 1740s. Finery forges with three or four waterwheels to drive bellows and hammers needed more water than a furnace at times, although continuity was not as important. They tended to be sited downstream from a furnace if they were in the same valley. Ponds were created by building a dam known as a pond bay, which often served as a road, across one of the many valleys in the undulating Wealden landscape. In 1754 one furnace was so drought-stricken that its manager considered hiring workmen to turn the wheel as a treadmill. This need for continuous water power was an incentive in the development of the water-returning engine, a waterwheel driven by water raised by a steam engine pump. Prehistoric ironmaking So far only about two dozen sites have been identified where iron was made before the Roman invasion, mostly scattered across East Sussex and the Vale of Kent. A large site at Broadfield, Crawley is the westernmost place where smelting has been ascertained, although there is a possible site associated with an Iron Age enclosure at Piper's Copse near Northchapel in the western Weald. Continuity of pottery styles from the Iron Age into the early Roman period makes precise dating of many sites to before or after the Roman conquest difficult. Carbon dating has identified a site at Cullinghurst Wood, Hartfield to between 350 and 750 BC. During his invasions of Britain in 55 and 54 BC Julius Caesar noted iron production near the coast, possibly at known sites at Sedlescombe and Crowhurst Park near Hastings. Roman ironmaking The Romans made full use of the brown- and ochre-coloured stone in the Weald, and many of their roads there are the means of transport for the ore, and were extensively metalled with slag from iron smelting. The sites of about 113 bloomeries have been identified as Roman, mainly in East Sussex. The Weald was in this period one of the most important iron-producing regions in Roman Britain. Excavations at a few sites have produced tiles of the Classis Britannica, suggesting that they were actually run by, or were supplying iron to this Roman fleet. Total iron production has been estimated at 750 tons per year, but under 200 tons per year after 250 AD. Medieval The invasion