Medieval demography is the study of human demography in Europe and the Mediterranean during the Middle Ages. It estimates and seeks to explain the number of people who were alive during the Medieval period, population trends, life expectancy, family structure, and related issues. Demography is considered a crucial element of historical change throughout the Middle Ages. The population of Europe remained at a low level in the Early Middle Ages, boomed during the High Middle Ages and reached a peak around 1300, then a number of calamities caused a steep decline, the nature of which historians have debated. Population levels began to recover around the late 15th century, gaining momentum in the early 16th century. The science of medieval demography relies on various lines of evidence, such as administrative records, wills and other types of records, archaeological field data, economic data, and written histories. Because the data are often incomplete and/or ambiguous, there can be significant disagreement among medieval demographers. Demographic history of Europe The population levels of Europe during the Middle Ages can be roughly categorized: 400–600 (Late Antiquity): population decline 600–1000 (Early Middle Ages): stable at a low level, with intermittent growth. 1000–1250 (High Middle Ages): population boom and expansion. 1250–1348 (Late Middle Ages): stable or intermittently rising at a high level, with fall in 1315–17 in England. 1348–1420 (Late Middle Ages): steep decline in England and France, growth in East Central Europe. 1420–1470 (Late Middle Ages): stable or intermittently falling to a low level in Western Europe, growth in East Central Europe. 1470–onward: slow expansion gaining momentum in the early 16th century. Late Antiquity Late Antiquity saw various indicators of Roman civilization beginning to decline, including urbanization, seaborne commerce, and total population. Only 40% as many Mediterranean shipwrecks have been found for the 3rd century as for the 1st. During the period from 150 to 400, with the intermittent appearance of plague, the population of the Roman Empire ranged from a high of 70 to a low of 50 million, followed by a fairly good recovery if not to the previous highs of the Early Empire. Serious gradual depopulation began in the West only in the 5th century and in the East due to the appearance of bubonic plague in 541 after 250 years of economic growth after the troubles which afflicted the empire from the 250s to 270s. Proximate causes of the population decrease include the