too naturally reduced the general level of peasant income, the surplus available for potential investment in agriculture, and the slim hope of agricultural innovation." As a result, on account of the social and economic system, the size of Europe’s population was limited; the existing agricultural system and technology could not support a population beyond a certain size. When the population of Europe surpassed the threshold that the existing economic structure permitted: population loss, social instability, and famine could result. Only through modifying the existing social structure of land ownership and distribution could Europe’s population surpass early 14th century levels. The above paragraphs are a synopsis of Brenner’s argument. The 1976 article has the full text of his original argument. He also wrote a book after that article. Regardless of the cause, populations continued to fall into the 15th century and remained low into the 16th because the plague returned in cycles over the course of the fourteenth and fifteenth centuries, although subsequent plagues, such as the "children’s plagues" of the 1360s were less virulent than the Great Plague of 1347-1348. Science and art of medieval demography Sources traditionally used by modern demographers, such as marriage, birth and death records, are often not available for this period, so scholars rely on other sources, such as archaeological surveys, and written records when available. Examples of field data include the physical size of a settlement, and how it grows over time, and 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, archaeological data are often difficult to interpret. It is often difficult to assign a precise age to discoveries. Also, some of the largest and most important sites are still occupied and cannot be investigated. Available archaeological records may be concentrated on 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 these limitations, much of our knowledge comes from written records: descriptive and administrative accounts. Descriptive accounts include those of chroniclers who wrote about the size of armies, victims of war or famine, participants in an oath. However these cannot be relied on as accurate, and are most useful as supporting evidence rather than being taken factually on their own. The most important written accounts are