most of the south of Britain that would eventually become England. Late medieval society After the Norman conquest of England in 1066, society seemed fixed and unchanging for several centuries, but gradual and significant changes were still taking place, the exact nature of which would not be appreciated until much later. The Norman lords spoke Norman French, and in order to work for them or gain advantage, the English had to use the Anglo-Norman language that developed in England. This became a necessary administrative and literary language (see Anglo-Norman literature), but despite this the English language was not supplanted, and after gaining much in grammar and vocabulary began in turn to replace the language of the rulers. At the same time the population of England more than doubled between Domesday and the end of the 13th century, and this growth was not checked by the almost continual foreign warfare, crusades and occasional civil anarchy. Feudalism, although historians debate the term, is often used to describe medieval society. Basically stated, a lord owns land or a fief which he allows vassals to work in return for their military service. The vast majority of the people were peasants who would work on the vassal's fiefs. This or a similar system was the basis of later medieval society. It probably existed in some form in England before the Norman conquest, but the Normans did much to institute it, either replacing existing lords or by becoming 'overlords' above now-demoted lords. A wealth of information on these social structures can be drawn from the best early surveys of its type, the Domesday Book. Church The Crusades are one measure of the ever-increasing power of the church in medieval life, with some estimates suggesting that as many as 40,000 clergy were ordained during the 13th century. This is also shown by the spate of cathedral building, common throughout Europe, at the time. These great buildings would often take several generations to complete, spawning whole communities of artisans and craftsmen and offering them jobs for life. A quarter of the land was owned by the Church. Its monasteries owned large tracts of land farmed by peasants. Prosperity and population growth The two centuries from 1200 to 1400 (when the plague hit) were prosperous. The population grew rapidly, from about 2 million to about 5 million. England remained a mainly rural society, and many agricultural changes, such as