Medieval demography
Medieval demography is the study of human demography in Europe during the Middle Ages. It is an estimate of the number of people who were alive during the Medieval period, population trends and movements. In many ways, demography was one of the most crucial factors of historical change throughout the Middle Ages.

# Demography
The population levels of Europe during the Middle Ages can be roughly categorized:
- 400-1000: stable at a low level.
- 1000-1250: population boom and expansion.
- 1250-1350: stable at very high level.
- 1350-1420: steep decline
- 1420-1470: stable at a low level.
- 1470-onward: slow expansion gaining momentum in the early 16th century.
As the ancient world came to an end there was a steep decline in population, reaching its lowest point around 542 with the bubonic plague (the Plague of Justinian, the last great plague in Europe until the Black Death of the 14th century). Estimates of total population of Europe are speculative, but at the time of Charlemagne it is thought to be between 25 and 30 million, and of this 15 million are in Carolingian France. Unlike the frontier settler image of a lone self-sufficient farmer who moves when he sees smoke from the neighbor's chimney, medieval settlements were thickly populated, with large zones of unpopulated wilderness in between. To be alone in the Middle Ages, and not part of a community, carried great risks. Crowded communities existed as islands in a sea of uncultivated wilderness.
In the 11th century, people began to move outward into the wilderness, in what is known as the "great clearances". During the High Middle Ages, forests and marshes were cleared and cultivated. At the same time, settlements moved beyond the traditional boundaries of the Frankish Empire to new frontiers in eastern Europe, beyond the Elbe River. Crusaders expanded to the Crusader States, the Iberian Peninsula was reconquered from the Moors, and the Normans colonized southern Italy. These movements and conquests are part of larger pattern of population expansion and resettlement that occurred in Europe at this time .
Reasons for this expansion and colonization include an improving climate known as the Medieval warm period allowing longer and more productive growing seasons; the end of barbarian raids by Vikings, Arabs, and Magyars resulting in greater political stability; advancements in medieval technology allowing more land to be farmed; reforms of the Church in the 11th century further increasing social stability; and the rise of Feudalism, which also brought increased social stability and thus more mobility. Nobles encouraged colonization. The bonds of serfdomthat tied peasants to the land began to weaken with the rise of a money economy. Land was plentiful while labor to clear and work the land was scarce; lords who owned the land found new ways to attract and keep labor. Urban centers began to emerge, able to attract serfs with the promise of freedom. As new regions were settled, both internally and externally, population naturally increased.
By 1300 Europe had become, some say, overpopulated. England, which had around 1 million people in 1086, was estimated to have a population that ranges from 5 to 7 million. France in 1328 (which was geographically smaller than France is today) was believed to have between 18 to 20 million people, which it would not surpass again until the early modern period. The region of Tuscany had 2 million people in 1300, which it would not reach again until 1850. Overall, the population of  Europe is believed to have reached a peak of 70 to 100 million. By comparison, the 25 member-states of the European Union in 2007 had a population of 494 million. This compares to grain yields that in the 14th century were between 2:1 and 7:1 (2:1 means for every seed planted, 2 are harvested). Modern grain yields are 30:1 or more, but the population is only 5-7 times higher.
By the 14th century the frontiers had ceased to expand and internal colonization was coming to an end, but population levels remained high. Then in the 14th century a number of calamities struck that devastated millions. Starting with the Great Famine in 1315, then the Hundred Years' War and the Black Death of 1348-1350, the population of Europe plummeted.
The period between 1348 and 1420 witnessed the heaviest loss. In Germany, about 40% of the named inhabitants disappeared. The population of Provence was reduced by 50% and in some regions in Tuscany 70% were lost during this period.
Historians have struggled to explain how so many could have died. There are problems with the long-standing theory that it was just caused by a medical illness (see further discussions at Black Death) and so social factors are looked at. A classic Malthusian argument has been put forward that says Europe was overcrowded with people, even in good times it was barely able to feed its population. A gradual malnutrition developed over decades lowering resistance to disease, and competition for resources meant more warfare. In short, the catastrophes were Malthusian checks on a population too large for its available resources. However, critics say that if this were true, the sudden fall in population would have endowed the survivors with abundant resources that would enable them to recover quickly. This was not the case; populations continued to fall and remained low almost to the 16th century. Thus, classic Malthusian theory does not offer a fully satisfactory explanation.
The most recent, although still tentative, explanation goes like this: by 1250, the population peaked and competition for resources meant that there was a great imbalance between property owners and workers. Rents went up, and wages sank, the unequal distribution of wealth increased between rich and poor. The conditions of the poor became so bad, they achieved net zero population growth. The economic conditions of the poor also aggravated the calamities of the plague because they had no recourse, such as fleeing to a villa in the country like the nobles in the Decameron, the poor lived in crowded conditions and could not isolate the sick, and had weaker immunities from a lacking diet and difficult subsistence lifestyle. After the plague and other exogenous causes of population decline this caused wage increases because of a lower labor supply, and a redistribution of wealth; however this did not happen right away because property owners resisted change through wage freezes and price controls. The wage freezes and price controls were partly responsible for popular uprisings, such as the Peasants' Revolt of 1381, and not until the later 15th century did the lower classes start to gain benefits. By 1500 the total population of Europe was substantially below that of 200 years earlier, but all classes overall had a higher standard of living.

# Science and art of medieval demography
The science of medieval demography is a fairly new one, but one that has received considerable attention lately, in particular with interest in the social issues of the Middle Ages in the later part of the 20th century. Most modern scholarly works today contain a section or chapter on the demographics of a particular town, region or kingdom. Because the sources traditionally used for demographics, such as marriage, birth and death records are generally not available for this period, scholars rely on other sources, which can roughly be broken down in to two categories: field data (archaeological) and written records.
Examples of field data include the physical size of a settlement, and how it grows over time. The appearance, or disappearance, of settlements, for example after the Black Death the archaeological record shows the abandonment of upwards of 25% of all villages in Spain. However there are problems that limit the use of archaeological data. It is often difficult to assign a precise age to discoveries. As well, some of the largest and most important sites are still occupied and can not be investigated, thus limiting the archaeological record to the more peripheral regions, for example early Middle Ages Anglo-Saxon burials at Sutton Hoo, in East Anglia in England, for which otherwise no records exist.
Because of the limitations of field data, most of what is known about Medieval demographics comes from written records, which can be categorized into descriptive accounts, and administrative accounts. Descriptive accounts include those left by chroniclers when they wrote of the size of armies, victims of war or famine, participants in an oath. However, many of these accounts were embellishments, and thus act as supporting evidence and never taken factually on their own.
The most important written accounts are those taken from administrative records. These accounts are more objective and accurate because the motivations for writing them were not to influence others. These records can be divided in to two categories: surveys and serial documents. Surveys cover an estate or region on a particular date, rather like a modern inventory. Manorial surveys were very common throughout the Middle Ages, in particular in France and England, but faded as serfdom gave way to a money economy. Fiscal surveys came with the rise of the money economy, the most famous and earliest being the Domesday Book in 1086. The Book of Hearths from Italy in 1244 is another example. The largest fiscal survey was of France in 1328. As kings continued to look for new ways to raise money, these fiscal surveys increased in number and scope over time. Surveys have limitations, because they cover only a snapshot in time they do not give long term trends, and they tend to exclude elements of society.
Serial records come in different forms. The earliest are from the 8th century and are land conveyances such as sales, exchanges, donations, and leases. Other types of serial records include death records from religious institutions and baptism registrations.  Other helpful records include heriots, court records, food prices and rent prices, from which inferences can be made.