The Black Death is thought to have originated in the arid plains of central Asia, where it then travelled along the Silk Road, reaching the Crimea by 1343. From there, it was most likely carried by Oriental rat fleas living on the black rats that were regular passengers on merchant ships. Spreading throughout the Mediterranean and Europe, the Black Death is estimated to have killed 30–60% of Europe's total population. All in all, the plague reduced the world population from an estimated 450 million down to 350–375 million in the 14th century.
The aftermath of the plague created a series of religious, social, and economic upheavals, which had profound effects on the course of European history. It took 150 years for Europe's population to recover. The plague recurred occasionally in Europe until the 19th century.
Origins of the disease
Main article: Black Death migration
The plague disease, caused by Yersinia pestis, is enzootic (commonly present) in populations of fleas carried by ground rodents, including marmots, in various areas including Central Asia, Kurdistan, Western Asia, Northern India and Uganda. Nestorian graves dating to 1338–9 near Lake Issyk Kul in Kyrgizstan have inscriptions referring to plague and are thought by many epidemiologists to mark the outbreak of the epidemic, from which it could easily have spread to China and India. In October 2010, medical geneticists suggested that all three of the great waves of the plague originated in China. In China, the 13th century Mongol conquest caused a decline in farming and trading. However, economic recovery had been observed at the beginning of the 14th century. In the 1330s a large number of natural disasters and plagues led to widespread famine, starting in 1331, with a deadly plague arriving soon after. Epidemics which may have included plague killed an estimated 25 million Chinese and other Asians during the 15 years before it reached Constantinople in 1347. However, according to George Sussman, the first obvious medical description of plague in China dates to 1644.
The disease may have travelled along the Silk Road with Mongol armies and traders or it could have come via ship. By the end of 1346, reports of plague had reached the seaports of Europe: "India was depopulated, Tartary, Mesopotamia, Syria, Armenia were covered with dead bodies".
Plague was reportedly first introduced to Europe at the trading city of Caffa in the Crimea in 1347. After a protracted siege, during which the Mongol army under Jani Beg was suffering from the disease, the army catapulted the infected corpses over the city walls to infect the inhabitants. The Genoese traders fled, taking the plague by ship into Sicily and the south of Europe, whence it spread north. Whether or not this hypothesis is accurate, it is clear that several existing conditions such as war, famine, and weather contributed to the severity of the Black Death.
The seventh year after it began, it came to England and first began in the towns and ports joining on the seacoasts, in Dorsetshire, where, as in other counties, it made the country quite void of inhabitants so that there were almost none left alive. ... But at length it came to Gloucester, yea even to Oxford and to London, and finally it spread over all England and so wasted the people that scarce the tenth person of any sort was left alive.
Geoffrey the Baker,