Paper mill  A paper mill is a factory devoted to making paper from vegetable fibres such as wood pulp, old rags, and other ingredients. Prior to the invention and adoption of the Fourdrinier machine and other types of paper machine that use an endless belt, all paper in a paper mill was made by hand, one sheet at a time, by specialized laborers. Historical investigations into the origin of the paper mill are complicated by differing definitions and loose terminology from modern authors: Many modern scholars use the term to refer indiscriminately to all kinds of mills, whether powered by humans, by animals or by water. Their propensity to refer to any ancient paper manufacturing centre as a "mill", without further specifying its exact power drive, has increased the difficulty of identifying the particularly efficient and historically important water-powered type. The use of human and animal powered mills was known to Muslim and Chinese papermakers. However, evidence for water-powered paper mills is elusive among both prior to the 11th century. The general absence of the use of water-powered paper mills in Muslim papermaking prior to the 11th century is suggested by the habit of Muslim authors at the time to call a production center not a "mill", but a "paper manufactory". Scholars have identified paper mills in Abbasid-era Baghdad in 794–795. The evidence that waterpower was applied to papermaking at this time is a matter of scholarly debate. In the Moroccan city of Fez, Ibn Battuta speaks of "400 mill stones for paper". Since Ibn Battuta does not mention the use of water-power and such a number of water-mills would be grotesquely high, the passage is generally taken to refer to human or animal force. An exhaustive survey of milling in Al-Andalus did not uncover water-powered paper mills, nor do the Spanish books of property distribution ("Repartimientos") after the Christian reconquest refer to any. Arabic texts never use the term mill in connection with papermaking and the most thorough account of Muslim papermaking at the time, the one by the Zirid Sultan Al-Muizz ibn Badis, describes the art purely in terms of a handcraft. Donald Hill has identified a possible reference to a water-powered paper mill in Samarkand, in the 11th-century work of the Persian scholar Abu Rayhan Biruni, but concludes that the passage is "too brief to enable us to say with certainty" that it refers to a water-powered paper mill.