crop rotation, kept the countryside profitable. Most people lived by farming, although there were wide variations in patterns of land ownership and the status of peasants. To meet the needs of the growing population more land had to be cultivated. Waste land was exploited and major incursions were made into forests, fen and marsh lands. "High farming" was increasingly practised, whereby the landowner took personal control of his land using hired hands rather than leasing it out. Treatises appeared on the best practices, but the growth of per-acre productivity was small. On good land one acre might produce 17 bushels of wheat (compared to 73 bushels an acre in the 1960s), or 26 of barley or 22 of oats. After 1300 prosperity was more tenuous owing to a combination of over-population, land shortages and depleted soils. The loss of life in the Great Famine of 1315–1317 shook the English economy severely, and population growth ceased. The first outbreak of the Black Death in 1348 then killed around half the English population, but left plenty of land for the survivors. The agricultural sector shrank, with higher wages, lower prices and shrinking profits leading to the final demise of the old demesne system and the advent of the modern farming system of cash rents for lands. Wat Tyler's Peasants' Revolt of 1381 shook the older feudal order and limited the levels of royal taxation considerably for a century to come. Towns The increase in population led not only to denser rural areas but also to more and larger towns. Many new towns appeared but most were small. Major cities such as Lincoln, Norwich and Thetford had 4,000–5,000 population, while London grew from 10,000 to nearly 40,000 population and York approached 10,000. The 13th century experienced a mini-industrial revolution, with the increased use of wind power and changes in the wool industry. Wool, always important to the British economy, was traditionally exported to be processed, but it was now frequently processed in England, creating a variety of extra jobs. The export of cloth continued to increase from the 14th century onwards, and after the closing of the port of Calais (which consumed much of the raw wool) by the Spanish in the late 16th century, cloth became the primary type of wool exported. Many people were finding different roles and responsibilities within English society too, with the growth of common law giving people