Slaves were not cheap, and the milling of enough flour by hand became increasingly expensive. At first the grain was ground by being rubbed between two stones known as querns. The grain would rest on a stone with a concave upper face and would be rubbed with a large smooth pebble. The next stage was to shape a bottom quern and to have a top stone which matched it and which could be pushed from side to side over the grain. By making both upper and lower stones circular, and by fixing a handle in the upper stone, a rotary motion was imparted to the hand quern. From that it is a short step to mounting the quern on a frame and having a long handle to rotate the upper millstone.
The first attempt to power millstones with water resulted in a form of watermill which we now call the Greek or Norse mill (see Glossary). In this the two millstones—derived from rotary hand-processing—were mounted over a stream with a high rate of fall. The lower millstone was pierced and mounted firmly in the mill, and the upper (runner) millstone was carried on a rotating spindle which passed through the lower millstone. This spindle was driven by a horizontal waterwheel which was turned by the thrust of water on its blades, paddles or spoon-shaped buckets. The stream was arranged, possibly by damming, to give a head of water, and this head produced a jet of water which hit and turned the paddles of the horizontal waterwheel. The horizontal watermill was a machine, albeit primitive, which ground grain faster than it could be ground by hand, and soon improvements began which further increased the speed of grinding.
The Romans adopted the Greek mill and made the hand mill more profitable by turning it into a horse-driven mill. Roman Europe became a civilization in which the countryside supported a growing number of larger towns. The use of slaves or servants to grind the grain for the family became too expensive, and there was a real need to increase the production of meal from the millstones. The often-quoted example of the range of ass-driven hourglass mills in Pompeii (see p. 262) shows how a town bakery was able to produce large quantities of meal for sale or for a baker’s shop. The Romans are thought to have been the inventors of the vertical waterwheel. In this system a waterwheel is turned in a vertical plane about a horizontal shaft and the millstones are driven from this by means of gear wheels. About 25 BC Vitruvius wrote De Architecture, and in the tenth book he describes the vertical waterwheel and its gear drive to the millstones. The earliest form of mill in which a single pair of millstones is driven by a waterwheel is therefore known as the Vitruvian mill.
Many examples of the Vitruvian mill have come to light in archaeological excavations. The most famous of all the Roman Vitruvian mills is the group at Barbegal near Arles, in the Bouches-du-Rhône department of France. Here an aqueduct and channel delivered water to a chamber at the top of a steep slope. The water descended in two parallel streams, and between the streams there were the mill buildings. There were sixteen overshot waterwheels in two rows of eight, the water from one wheel driving the next one below it. This example from c. AD 300 shows a sophistication in millwrighting design which typifies the Roman approach to many of their problems of engineering and architecture. There are representations of vertical waterwheels in Byzantine art and in the Roman catacombs. By Hadrian’s Wall in 1903, Dr Gerald Simpson excavated a Roman watermill which dates from c. AD 250. Lord Wilson of High Wray prepared drawings of this which were published in Watermills and Military Works on Hadrian’s Wall in 1976. Similar and more important excavations, carried out in Rome in the 1970s by Schiøler and Wikander, show how universal the spread of the Vitruvian mill was in the Roman period.
Further archaeological evidence confirms the presence of Roman watermills in Saalburg, near Bad Homburg in Germany, and Silchester, Hampshire. The Romans and their colonials were among the first people to dig mines for metals. In some of these deep mines there was a need to install mechanical waterraising devices and in the mines at Rio Tinto in south-west Spain a substantial water-lifting wheel has been found. While this is not strictly a waterdriven wheel it is analogous. The large rim carries a series of wooden boxes which have side openings at the upper ends. The wheel is turned by men pulling on the spokes and the boxes lift the water so that it empties out at high level into a trough which leads it away from the wheel. This wheel is one form of water-raising device and its derivatives still exist in parts of Europe and the Near East. The best-known examples are those at Hama in Syria, where waterdriven wheels carry containers on the rim which raise the water to the top of the wheel where it empties out into irrigation channels. The biggest of these is 19.8m (65ft 6in) in diameter
Fertilizers Revolutionizes the Traditional Farming
