generally believed that Rome could only be fed and maintained with Egyptian aid". However, he argued that "Now [that] we have returned the Nile its riches... her business is not to allow us food but to pay a proper tribute. Mechanization The Romans improved crop growing by irrigating plants using aqueducts to transport water. Mechanical devices aided agriculture and the production of food. Extensive sets of mills existed in Gaul and Rome at an early date to grind wheat into flour. The most impressive extant remains occur at Barbegal in southern France, near Arles. Sixteen overshot water wheels arranged in two columns were fed by the main aqueduct to Arles, the outflow from one being the supply to the next one down in the series. The mills apparently operated from the end of the 1st century AD until about the end of the 3rd century. The capacity of the mills has been estimated at 4.5 tons of flour per day, sufficient to supply enough bread for the 12,500 inhabitants occupying the town of Arelate at that time. Vertical water wheels were well known to the Romans, described by Vitruvius in his De architectura of 25 BC, and mentioned by Pliny the Elder in his Naturalis Historia of AD 77. There are also later references to floating water-driven grain mills in Rome and Byzantium and to water-driven sawmills on the river Moselle by the poet Ausonius. Multiple stacked sequences of reverse overshot water-wheels were used to provide motive power in many Roman mines. There is evidence from bas-reliefs that farmers in northern Gaul (present day France) used a kind of automatic harvester or reaper when collecting ripe grain crops. The machine, called the "vallus" or "gallic vallus", was apparently invented and used by the Treveri people. It cut the ears of grain without the straw and was pushed by oxen or horses. Pliny the Elder mentions the device in the Naturalis Historia XVIII, 296. Possibly because the vallus was cumbersome and expensive, its adoption never became widespread and it fell into disuse after the 4th century CE. Scythes and sickles were the usual tools for harvesting crops. Acquiring a farm Aristocrats and common people could acquire land for a farm in one of three ways. The most common way to gain land was to purchase the land. Though some lower-class citizens did own small pieces of land, they often found it