justinian is said to have been "completed" in the middle of the 8th century. because the infectious disease spread inland by the transferring of merchandise through justinian's efforts in acquiring luxurious goods of the time and exporting supplies, his capital became the leading exporter of the bubonic plague. procopius, in his work secret history, declared that justinian was a demon of an emperor who either created the plague himself or was being punished for his sinfulness. second pandemic main articles: black death and second plague pandemic citizens of tournai bury plague victims. miniature from the chronicles of gilles li muisis (1272–1352). bibliothèque royale de belgique, ms 13076–77, f. 24v. people who died of bubonic plague in a mass grave from 1720 to 1721 in martigues, france in the late middle ages europe experienced the deadliest disease outbreak in history when the black death, the infamous pandemic of bubonic plague, hit in 1347, killing one-third of the european human population. some historians believe that society subsequently became more violent as the mass mortality rate cheapened life and thus increased warfare, crime, popular revolt, waves of flagellants, and persecution. the black death originated in central asia and spread from italy and then throughout other european countries. arab historians ibn al-wardni and almaqrizi believed the black death originated in mongolia. chinese records also show a huge outbreak in mongolia in the early 1330s. in 2022, researchers presented evidence that the plague originated near lake issyk-kul in kyrgyzstan. the mongols had cut the trade route (the silk road) between china and europe, which halted the spread of the black death from eastern russia to western europe. the european epidemic may have begun with the siege of caffa, an attack that mongols launched on the italian merchants' last trading station in the region, caffa in the crimea. in late 1346, plague broke out among the besiegers and from them penetrated the town. the mongol forces catapulted plague-infested corpses into caffa as a form of attack, one of the first known instances of biological warfare. when spring arrived, the italian merchants fled on their ships, unknowingly carrying the black death. carried by the fleas on rats, the plague initially spread to humans near the black sea and then outwards to the rest of europe as a result of people fleeing from one area to another. rats migrated with humans, traveling among grain bags, clothing, ships, wagons, and grain husks. continued research indicates that black rats, those that primarily transmitted the disease, prefer grain as a primary meal. due to this, the major bulk grain fleets that transported major city's food shipments from africa and alexandria to heavily populated areas, and were then unloaded by hand, played a role in increasing the transmission effectiveness of the plague. third pandemic the plague resurfaced for a third time in the mid-19th century; this is also known as "the modern pandemic". like the two previous outbreaks, this one also originated in eastern asia, most likely in yunnan, a province of china, where there are several natural plague foci. the initial outbreaks occurred in the second half of the 18th century. the disease remained localized in southwest china for several years before spreading. in the city of canton, beginning in january 1894, the disease had killed 80,000 people by june. daily water-traffic with the nearby city of hong kong rapidly spread the plague there, killing over 2,400 within two months during the 1894 hong kong plague. the third pandemic spread the disease to port cities throughout the world in the second half of the 19th century and the early 20th century via shipping routes. the plague infected people in chinatown in san francisco from 1900 to 1904, and in the nearby locales of oakland and the east bay again from 1907 to 1909. during the former outbreak, in 1902, authorities made permanent the chinese exclusion act, a law originally signed into existence by president chester a. arthur in 1882. the act was supposed to last for 10 years, but was renewed in 1892 with the geary act, then followed by the 1902 decision. the last major outbreak in the united states occurred in los angeles in 1924, though the disease is still present in wild rodents and can be passed to humans that come in contact with them. according to the world health organization, the pandemic was considered active until 1959, when worldwide casualties dropped to 200 per year. in 1994, a plague outbreak in five indian states caused an estimated 700 infections (including 52 deaths) and triggered a large migration of indians within india as they tried to avoid the disease. it was during the 1894 hong kong plague outbreak that alexandre yersin isolated the bacterium responsible (yersinia pestis), a few days after japanese bacteriologist kitasato shibasaburō had isolated it. however, the latter's description was imprecise and also expressed doubts of its relation to the disease, and thus the bacterium is today only named after yersin. society and culture contemporary engraving of marseille during the great plague in 1720 copper engraving of a plague doctor from the 17th century. this is one of the most well-known representations in art of the bubonic plague the scale of death and social upheaval associated with plague outbreaks has made the topic prominent in many historical and fictional accounts since the disease was first recognized. the black death in particular is described and referenced in numerous contemporary sources, some of which, including works by chaucer, boccaccio, and petrarch, are considered part of the western canon. the decameron, by boccaccio, is notable for its use of a frame story involving individuals who have fled florence for a secluded villa to escape the black death. first-person, sometimes sensationalized or fictionalized, accounts of living through plague years have also been popular across centuries and cultures. for example, samuel pepys's diary makes several references to his first-hand experiences of the great plague of london in 1665–6. later works, such as albert camus's novel the plague or ingmar bergman's film the seventh seal have used bubonic plague in settings, such as quarantined cities in either medieval or modern times, as a backdrop to explore a variety of concepts. common themes include the breakdown of society, institutions, and individuals during the plague, the cultural and psychological existential confrontation with mortality, and the allegorical use of the plague about contemporary moral or spiritual questions. biological warfare some of the earliest instances of biological warfare were said to have been products of the plague, as armies of the 14th century were recorded catapulting diseased corpses over the walls of towns and villages to spread the pestilence. this was done by jani beg when he attacked the city of kaffa in 1343. later, plague was used during the second sino-japanese war as a bacteriological weapon by the imperial japanese army. these weapons were provided by shirō ishii's units and used in experiments on humans before being used in the field. for example, in 1940, the imperial japanese army air service bombed ningbo with fleas carrying the bubonic plague. during the khabarovsk war crime trials, the accused, such as major general kiyoshi kawashima, testified that, in 1941, 40 members of unit 731 air-dropped plague-contaminated fleas on changde. these operations caused epidemic plague outbreaks. continued research substantial research has been done regarding the origin of the plague and how it traveled through the continent. mitochondrial dna of modern rats in western europe indicated that these rats came from two different areas, one being africa and the other unclear. the research regarding this pandemic has greatly increased with technology. through archaeo-molecular investigation, researchers have discovered the dna of plague bacillus in the dental core of those that fell ill to the plague. analysis of teeth of the deceased allows researchers to further understand both the demographics and mortuary patterns of the disease. for example, in 2013 in england, archeologists uncovered a burial mound to reveal 17 bodies, mainly children, who had died of the bubonic plague. they analyzed these burial remains using radiocarbon dating to determine they were from the 1530s, and dental core analysis revealed the presence of yersinia pestis. other evidence for rats that are currently still being researched consists of gnaw marks on bones, predator pellets and rat remains that were preserved in situ. this research allows individuals to trace early rat remains to track the path traveled and in turn connect the impact of the bubonic plague to specific breeds of rats. burial sites, known as plague pits, offer archaeologists an opportunity to study the remains of people who died from the plague. another research study indicates that these separate pandemics were all interconnected. a current computer model indicates that the disease did not go away in between these pandemics. it rather lurked within the rat population for years without causing human epidemics.