Landscape with Watermill. A watermill or water mill is a mill that uses hydropower. It is a structure that uses a water wheel or water turbine to drive a mechanical process such as milling, rolling, or hammering. Such processes are needed in the production of many material goods, including flour, lumber, paper, textiles, and many metal products. These watermills may comprise gristmills, sawmills, paper mills, textile mills, hammermills, trip hammering mills, rolling mills, wire drawing mills. One major way to classify watermills is by wheel orientation, one powered by a vertical waterwheel through a gear mechanism, and the other equipped with a horizontal waterwheel without such a mechanism. The former type can be further divided, depending on where the water hits the wheel paddles, into undershot, overshot, breastshot and pitchback waterwheel mills. Another way to classify water mills is by an essential trait about their location: tide mills use the movement of the tide; ship mills are water mills onboard a ship. Watermills impact the river dynamics of the watercourses where they are installed. During the time watermills operate channels tend to sedimentate, particularly backwater. Also in the backwater area, inundation events and sedimentation of adjacent floodplains increase. Over time however these effects are cancelled by river banks becoming higher. Where mills have been removed, river incision increases and channels deepen. According to Terry S. Reynolds and R. J. Forbes, the water wheel may have originated from the ancient Near East in the 3rd century BC for use in moving millstones and small-scale grain grinding. Reynolds suggests that the first water wheels were norias and, by the 2nd century BC, evolved into the vertical watermill in Syria and Asia Minor, from where it spread to ancient Greece and the Roman Empire. S. Avitsur also supports a Near-Eastern origin for the watermill. Further information: List of ancient watermills Engineers in the Hellenistic world used the two main components of watermills, the waterwheel and toothed gearing, and, along with the Roman Empire, operated undershot, overshot and breastshot waterwheel mills. Early evidence of a water-driven wheel is probably the Perachora wheel, in Greece. An early written reference is in the technical treatises Pneumatica and Parasceuastica of the Greek engineer Philo of Byzantium. The British historian of technology M.J.T. Lewis has shown that those portions of Philo of Byzantium's mechanical treatise which describe water wheels and which have been previously regarded as later Arabic interpolations, actually date back to the Greek 3rd-century BC original. The sakia gear is, already fully developed, attested in a 2nd-century BC Hellenistic wall painting in Ptolemaic Egypt. Lewis assigns the date of the invention of the horizontal-wheeled mill to the Greek colony of Byzantium in the first half of the 3rd century BC, and that of the vertical-wheeled mill to Ptolemaic Alexandria around 240 BC. The Greek geographer Strabon reports in his Geography a water-powered grain-mill to have existed near the palace of king Mithradates VI Eupator at Cabira, Asia Minor, before 71 BC. The Roman engineer Vitruvius has the first technical description of a watermill, dated to 40/10 BC; the device is fitted with an undershot wheel and power is transmitted via a gearing mechanism. He also seems to indicate the existence of water-powered kneading machines. The Greek epigrammatist Antipater of Thessalonica tells of an advanced overshot wheel mill around 20 BC/10 AD. He praised for its use in grinding grain and the reduction of human labour: Hold back your hand from the mill, you grinding girls; even if the cockcrow heralds the dawn, sleep on. For Demeter has imposed the labours of your hands on the nymphs, who leaping down upon the topmost part of the wheel, rotate its axle; with encircling cogs, it turns the hollow weight of the Nisyrian millstones. If we learn to feast toil-free on the fruits of the earth, we taste again the golden age. The Roman encyclopedist Pliny mentions in his Naturalis Historia of around 70 AD water-powered trip hammers operating in the greater part of Italy. There is evidence of a fulling mill in 73/4 AD in Antioch, Roman Syria. Another Roman author Ausonius mentions a lot of watermills in the walley of Rhine and its tributaries in the 4th century.