The plague that hit London in spring 1665 was the last major outbreak of bubonic plague in England — the closing chapter of the European Yersinia pestis cycle that had begun with the Black Death of 1347–1351 and had recurred at intervals of roughly twenty years across the intervening three centuries. The 1665 outbreak killed approximately 70,000 to 100,000 Londoners between April and November — about a quarter of the city’s contemporary population of approximately 400,000.
It was not a small event. It was the largest single mortality event in English history before the First World War.
How it began
The first plague deaths of the 1665 outbreak were recorded in the parish of St Giles-in-the-Fields, on the northwestern edge of the contemporary built-up area (modern Covent Garden). The first two confirmed deaths were on 12 April 1665. The parish register notes the cause of death as plague — a classification the parish clerks of London had not had occasion to use in volume since the previous outbreak of 1647.
The disease spread along the western and northern edges of the City through May and June. The City of London’s parishes themselves, ringed by the Roman wall and connected to the western parishes by the densely-built Holborn corridor, started returning weekly plague deaths in late June. By the end of June the weekly Bills of Mortality — the printed weekly death summaries that London had published since the 1590s — were recording approximately 100 plague deaths per week and rising.
The mortality curve through the summer was approximately exponential. By the end of July the weekly Bills were recording approximately 2,000 plague deaths per week; by the end of August approximately 6,000; by the second week of September the peak weekly figure of approximately 8,300. The September peak was almost certainly an undercount: by that point the plague had killed enough of the parish clerks, sextons, and gravediggers responsible for compiling the Bills that the reporting infrastructure had partly collapsed.
What people did
The wealthy left. Charles II and the court evacuated to Salisbury in July, then to Oxford for the autumn and winter. Approximately two-thirds of the city’s senior nobility and gentry followed. The College of Physicians evacuated approximately half of its membership; the leading London merchants who could afford a country residence took it. The City of London government collapsed substantially under the combined pressure of the senior leadership leaving and the surviving leadership being unable to enforce the standard disease-control measures.
Those who stayed faced a substantially different city. The Privy Council, on the model of the 16th-century Italian plague-response tradition, ordered:
The closing of all theatres, taverns, and substantial public gatherings.
The killing of all dogs and cats within the city walls — approximately 40,000 dogs and an unknown larger number of cats were destroyed in the first weeks, on the (incorrect) theory that they were the principal vector of transmission. The actual vector — fleas living on the city’s rat population — was substantively encouraged by the cat purge.
The quarantine of plague houses: any house with a plague death had a red cross painted on the door, with the inscription LORD HAVE MERCY UPON US, and was sealed for forty days with all surviving occupants inside. Watchmen were posted to enforce the quarantine. The death rate inside sealed houses was approximately 100%.
The disposal of plague dead in mass graves — plague pits — at the edges of the parishes. The largest of these, at Aldgate and at Bunhill Fields north of the City wall, held tens of thousands of bodies. The pits were re-discovered repeatedly during 19th- and 20th-century London construction work; portions remain undisturbed beneath modern streets.
The provision of plague hospitals — pesthouses — outside the city walls, primarily at Soho, Westminster, and Stepney. These functioned as places to die rather than to be cured. Recovery rates were approximately 10–20%.
The professional response
The medical response was confused. The leading London medical authority of the period — the College of Physicians — produced multiple competing theories of plague causation and treatment, none of which had any therapeutic effect. The dominant theory was miasmatic: bad air, rising from the accumulations of refuse and decaying organic matter in the medieval city, was thought to carry the plague directly to the human respiratory system. The recommended preventive measures involved burning aromatic herbs, carrying scented pomanders, and avoiding crowded public spaces.
The most prominent physician of the outbreak was Dr Nathaniel Hodges, a College of Physicians fellow who chose to remain in London for the duration. His 1672 account Loimologia is the most-detailed contemporary medical narrative of the outbreak; it is also the most source for the failure of the period’s medical understanding to make any therapeutic progress. Hodges himself survived; about two-thirds of the College fellows who remained in London did not.
The most-famous lay account is Samuel Pepys’s Diary — the entries from June 1665 through February 1666 document the experience of an Admiralty official who remained at his post in London for the duration of the outbreak, watching the deaths of acquaintances, the closures of his usual social venues, and the progressive emptying of the city. Pepys himself survived (he died in 1703).
The most-famous literary treatment is Daniel Defoe’s A Journal of the Plague Year, published in 1722 — a-invented first-person narrative based on Defoe’s research in the surviving Bills of Mortality, supplemented by his uncle’s contemporary diary and by oral histories collected from elderly Londoners who had been children during the 1665 outbreak.
How it ended
The autumn mortality curve broke in late September. The October Bills returned approximately 5,000 weekly plague deaths; the November Bills approximately 1,500; the December Bills approximately 200. By March 1666 the weekly plague deaths were approximately zero. The standard period explanation was that cold weather had killed the disease. The modern explanation is approximately the same: cold temperatures reduced the flea population on which the Yersinia pestis bacterium depends for transmission, and the surviving Londoners had either developed immunity or moved out of the most-affected districts.
The total mortality estimate of approximately 70,000–100,000 is necessarily approximate. The 1665 Bills of Mortality recorded approximately 68,000 plague deaths, but the Bills were undercounting from the late-August peak onward. Modern epidemiological estimates based on substitution-rate analysis of the surviving parish registers suggest the true mortality was probably closer to 100,000.
What happened next
Approximately six months after the last plague death of the 1665 outbreak, the Great Fire of London (2–5 September 1666) destroyed approximately 80% of the City of London’s built environment. Most of the parishes that had been worst-affected by the plague — the densely-built medieval districts inside the Roman wall — were among the destroyed. The rebuild replaced the medieval timber-frame construction with brick and stone, with wider streets and improved sanitation. The combination of the rebuild and the broader 17th-century changes in European rat populations (the-smaller and more rural Rattus rattus being displaced by the larger and more urban Rattus norvegicus) is the leading explanation for why no further major plague outbreak ever hit England.
The 1720 outbreak in Marseille was the last major plague event in Western Europe. The disease still circulates in rural rodent populations in Africa, Asia, and the American Southwest; approximately 1,000–2,000 human cases per year are still reported globally, mostly treatable with modern antibiotics. The European Yersinia pestis cycle that began in 1347 ended in London in autumn 1665.