# The dancing plague of 1518 (Strasbourg)

Published report: https://historical-mysteries.netlify.app/dancing-plague/report
Local copy: `report.html` in this folder, identical to the published page.

## The mystery

On 14 or 15 July 1518, in Strasbourg, then a free city of the Holy Roman Empire on the Rhine, a woman began to dance in the street and kept it up for days. The city council had her taken to a shrine of St Vitus, the saint believed both to send this sickness and to cure it, in the hills above Saverne to the north-west; while she was on the road, others began to dance, about thirty-four within four days. The council banned drums and pipes, lodged the dancers in guild halls, sent them to the shrine by wagon on 23 July, told its bishop on 25 July that the physicians called it a natural illness of the heat and the stars, banned all public dancing on 2 August, and voted a hundredweight candle for the saint on 31 August. Its decree speaks of up to fifty dancing at once; a family chronicle written at the time counts more than two hundred over four weeks.

The cause was not diagnosed in 1518 and is still disputed. The physicians said natural illness; the chroniclers of the next century said a curse, a punishment and fraud; E. Louis Backman, a Swedish physician and historian of religious dance, proposed in 1952 that they were poisoned by ergot, a fungus of rye whose poison causes convulsions and gangrene, and that became the popular explanation; John Waller, a historian of medicine, argued in 2008 for a trance brought on by hunger, fear and belief in the saint's curse, spread by sight; Gregor Rohmann, a German medievalist, and Robert Bartholomew, a sociologist of mass hysteria, read the dancing as a religious rite. The facts are disputed too: the popular story has four hundred dancers, fifteen deaths a day, a first dancer named Frau Troffea and a council that hired musicians to keep the sick dancing, while the surviving texts give figures from fifty to four hundred and the council's own minutes burned in 1870.

The case was judged by reading every text that describes the dancing in the order it was written, from the council's papers of 1518 to the chronicles of the following century, tracing each element of the modern story to the text in which it first appears, and testing the explanations against that record and against three kinds of evidence the earlier writers did not have: reconstructed weather for the growing seasons of 1515 to 1518, the grain prices of those years, and modern medical case series of outbreaks spread by suggestion. The result is below.

## Verdict and confidence

The dancing was a behavioural epidemic among the poor of a city at the end of two years of dearth. It spread by watching and by music, and it took its shape from the belief that St Vitus sends the dance and cures it. It was not ergot poisoning. The council counted up to fifty dancing at a time; a chronicle written at the time counted more than two hundred over four weeks. No text written between 1518 and about 1580 that we read records a death.

Evidence label: **Probable**. A behavioural epidemic is the probable cause: the evidence clearly favours it over the other explanations but does not prove it, and the percentage moves when the same evidence is weighed differently (about 85 in the base case, 55 in the most sceptical case).

- About 85 percent that the cause was behavioural rather than a poison or an infection.
- About 65 percent that it was, more exactly, a psychogenic epidemic (mass psychogenic illness of the motor type; "a natural illness" in the words of the physicians of 1518); about 20 percent that the dancing was a culturally scripted rite (the reading of the medical historian Alfred Martin in 1914, Bartholomew in 2000 and Rohmann in 2013). The line between those two is partly vocabulary.
- Ergot about 5 percent; another organic disease about 5 percent; mostly fraud and begging about 5 percent. All of these are judgments that depend on the five explanations weighed and on the weight given to each piece of evidence. They are not measurements.
- How the figures move (the table is printed next to the headline in the report): accepting the late reports of deaths by the chroniclers Daniel Specklin (about 1580) and Michael Kleinlawel (1625) as fact cuts the behavioural share to about 70; the most sceptical case, which also allows an ergot route through old granary stock and reads the physicians' diagnosis as an infection, leaves it at about 55, still leading, with ergot at 18 and another organic disease at 20. The statement that neither ergot nor another organic disease reaches ten percent holds for the base case only.

The size of the outbreak, in the texts written at the time: one unnamed woman on Wednesday 14 or Thursday 15 July 1518; about 34 dancers within four days (the chronicle of the Imlin family of Strasbourg); "uff fünfzig personen", up to fifty, afflicted at once in the council's own mandate of late July, a figure for one moment; "more than 200" over four weeks in the Imlin chronicle, the only running total from the period, and nothing in the record contradicts it; "over 100 at once" only in Specklin, about 1580. The two figures from 1518 measure different things, and the headline states both. The council restricted drums on 22 July, sent the sick to the shrine of St Vitus at the Hohlenstein, a hollow rock above Saverne, on 23 July, told the bishop on 25 July that the physicians called it a natural illness of the stars and the heat and that it was coming to an end, banned public dancing until Michaelmas on 2 August, made families and brotherhoods responsible for their sick on 11 August, and voted a hundredweight candle for the saint on 31 August. Nobody is recorded as having died in any of these texts. That is silence in the sources read, not proof that nobody died; no parish or hospital register was searched.

## Confirms, shifts or overturns

- Confirms, in the sense of agreeing with, the conclusions of the Strasbourg historians Élisabeth Clementz and Georges Bischoff, set out in the 2018 exhibition "1518, la fièvre de la danse" (about fifty dancers, no contemporary death, Troffea an invention of Paracelsus, ergot rejected), of the American historian Erik Midelfort (1999), and of Alfred Martin (1914) on the sources and the 1418 error. Also agrees with Waller's premise (a city in dearth and fear, borne out by the climate and price record) and with his account of how the dancing spread (by sight, as the commission minutes of 23 July describe).
- Shifts the popular account (Waller 2008 and 2009; Wikipedia): 400 dancers becomes up to 50 at a time and more than 200 over four weeks; "dozens of deaths" becomes none recorded in the sources read before about 1580; "fifteen dying a day" has one candidate source, the Augsburg merchant Wilhelm Rem's count in 1518 of fifteen new cases on one day ("ankam", came upon), and its descent into the modern death rate is our inference rather than a traced citation; the council that staged the dancing becomes a council that contained it (Specklin's chronicle of about 1580 is the only source for the stage). Clementz and Bischoff had already questioned how much contemporary testimony lies behind the familiar story and treated Troffea as a later invention; the report builds on that correction.
- Rejects ergot (Backman 1952) on eight counts: the season (onset before the 1518 harvest), the weather of the crop year (1517 was the third driest summer of the century at Strasbourg in the Old World Drought Atlas, a tree-ring reconstruction of summer soil moisture, with a dry spring and a warm flowering), the regional form of the disease, its clinical course, the way the dancing spread, the absence of recorded deaths, the physicians' diagnosis, and the end in August.
- Nothing here overturns what historians already think.

## What is new (as far as the literature we reached shows)

1. "Fifteen a day" has one candidate source: Wilhelm Rem's sentence of 1518, "daß ain tag wol bei 15 menschen ankam", a count of new cases rather than of deaths. Martin (1914, p. 114) quoted it only to fix the year. Waller's essay in the Lancet (February 2009, "about 15 lives a day"; further reading Backman and Midelfort only) and his book ("fifteen were dying each day") give a death rate; Wikipedia took it from the Lancet on 8 April 2016. The descent from Rem to Waller is an inference from the wording (Waller's endnote and Backman's translation were not seen), and the report says so. A new reading of a printed text.
2. 200 against 400: the Strasbourg librarian Rodolphe Reuss's 1875 edition of the Imlin chronicle from the manuscript reads "mehr dan 200" (page image checked); the Kleine Strassburger Chronik independently has "über 200"; 400 is the psychiatrist Georg Witkowski's reading of 1879, carried by Martin (1914), Midelfort (1999) and Waller.
3. The anonymous Basel chronicle (before 1537) restored to 1518: its manuscript reads 1518; its editor, the Basel historian August Bernoulli, moved it to 1418 in 1902 because the jurist Johann Schilter had printed the council's orders under that year in 1698. It is the earliest narrative outside Strasbourg, the prose twin of the verses Schilter printed, and the earliest source for "hundreds".
4. The ergot hypothesis tested against reconstructed weather, for the first time that we know of: a drought index of −6.8 for 1517 at Strasbourg in the Old World Drought Atlas (third driest summer of 1500–1600), a dry spring and a warm May and June; the cold June of 1518 is the one favourable sign, and it belongs to a crop not yet cut. The climate and price datasets are the one body of evidence not brought to the question before (the datasets are the published work of others; their application here is new). The extraction from the atlas was run a second time from scratch and gives the same value (−6.787 at the Strasbourg cell). Items 2, 3 and 5 to 9 are new readings of evidence already in print.
5. The outbreak ended in August: "Dienstag post Adolphi" is 31 August 1518 (St Adelphus falls on 29 August), rather than 29 September as Martin read it; the letter of 25 July says the sickness was ending.
6. The council's policy was containment rather than encouragement, and the pilgrimage was imposed by the council (the Instruction of 23 July), which weakens the reading of the dancing as a chosen rite.
7. Waller's supporting details corrected: the English sweating sickness of 1517 is a misdating of 1529; the "smallpox hospital" is the Blatterhaus, the house for syphilis; the leper house shows no surge; the Bundschuh of 1517 (a peasant plot on the Upper Rhine) was a conspiracy scare.
8. Two bad arguments retired: the claim that ergot alkaloids decay within a year (unsound), and the 1951 mass poisoning at Pont-Saint-Esprit in southern France as a case of ergot-induced mass behaviour (organic mercury, according to the European Food Safety Authority in 2012).
9. No Strasbourg record of dancers in 1374; the fifteenth-century cases on the Upper Rhine sorted (Zurich 1418 or 1428 and 1452, the cluster of 1463 under St John, the Rottweil curse of 1485).

## Where the report fell short

- The cathedral schoolmaster Hieronymus Gebwiler's contemporary account (ed. Stenzel 1926) was not read; it is known here through Midelfort and the 2018 exhibition's teachers' dossier.
- The letter of 25 July 1518 was read only in the French translation published in 2018; the mandate of 2 August is not transcribed anywhere we could reach.
- Witkowski's paper of 1879 was not found online. Backman's book of 1952 was not obtained (about sixty snippets from a library full-text search). Waller's articles in Endeavour, the Lancet and the Psychologist were read in full, but his book only in about 120 such snippets, so his endnote for "fifteen were dying each day" was not seen. Midelfort's chapter was read from the text of an archive.org scan whose provenance could not be confirmed.
- Rohmann's book of 2013 was not read (his 2020 article, reviews and an interview were used); Élisabeth Clementz's transcriptions of the 1518 documents in the 2018 catalogue (pp. 136–152) were not obtained.
- The Alsatian economic historian Charles-Auguste Hanauer's price volume of 1878 could not be opened; two later transcriptions disagree on the 1516 rye price.
- The gridded climate reconstructions have low skill before 1659; the drought value for 1517 is robust, the seasonal rainfall figures are not.
- Three words in the council's papers are unexplained ("pfrymen", "termen", "brucken" or "beucken").
- No parish or hospital register was searched; the absence of deaths is an argument from the silence of every text written at the time.

## Files

- `report.html`: the published report.
- `notes/`: A1_council_record.md (the council's papers and Wencker's extracts), A2_chronicles.md (the chronicles and how they descend from one another), B_paracelsus_and_retellings.md (Paracelsus, Hecker, Backman, Waller, the Wikipedia revision history), C_medical.md (ergot, psychogenic illness, modern case series), D_climate_harvest.md (climate, harvests, prices, famine), E_vitus_cult_and_precedents.md (the cult of St Vitus, the shrine, earlier outbreaks), verification_log.md (independent checks of the readings and figures).
- `sources/`: downloads, OCR text and page images, with index files A1_SOURCES.md, A2_SOURCES.md, B_SOURCES.md, medical/C_SOURCES.md, climate/D_SOURCES.md, context/E_SOURCES.md, and verified-page-images/README.md (nine readings checked against the page images).
- `data/`: extracts for Strasbourg from the Old World Drought Atlas and from the Pauling, Luterbacher and Xoplaki, Dobrovolný and Glaser reconstructions; Hanauer's prices in Allen's transcription and in Elsas's; summary_by_year_1512-1521.csv; owda_map_1515-1519.png.
- `code/`: extraction scripts for each dataset, make_summary_table.py, calendar_1518.py (weekdays of the Julian calendar for 1518), hocr2txt.py.