The composition derives from a lost work of Pieter Bruegel the Elder. Whether that prototype was a painting or drawing is unknown however, and its existence is presumed only through a group of three engravings of 1642 by Henricus Hondius. These divide the principle figures of the composition into three groups (in reverse), and are accompanied by a description of the events depicted: Vertooninge Hoe de Pelgerimmen, op s. Ians-dagh, buyten Brussel, tot Meulenbeeck danssen moeten, ende als sy over dese Brugh gedanst hebben, ofte gedwongen werden op desevolgende maniere, dan schijnen sy, voor een Iaer, van de vallende Sieckte, genesen te zijn ['Images of How the pilgrims, on Saint John's Day, outside Brussels, have to dance their way to Meulenbeeck, where, either willingly or forced, have to cross the bridge there, and they will be healed from disease for a year'].
Hondius's text then goes on to describe the various elements of the scene, and attribute the composition to 'den uytnemenden konstigen Schilder Pieter Breugel'. One might suppose, from that, that Hondius was accurately reflecting three separate compositions by Breugel (two of the engravings are also inscribed individually 'P. Breugel inv' and 'P.B. inv'). However, crucially Hondius' text also refers to how 'ende dan komen de Huyslieden van dier plaets, haer lavende, ende wat warms in-gevende [And then the villagers arrive who live near the bridge, and they provide the group with something to drink and something warm to eat]'. This evidently refers to figures walking just beyond the foreground procession represented here. It is likely that Pieter I's prototype was of slightly expanded dimensions, with other figures and a landscape beyond; Hondius himself then divided that for his series of engravings.
This undivided and enlarged composition, with added figures, is known in five works, including one picture signed by Pieter Brueghel II, sold at Christie’s, London, 6 December 2007, lot 26 (£216,500) and four drawings (Vienna, Albertina; Amsterdam, Rijksmuseum; Berlin, Staatliche Museen, and a much looser sketch recorded in the Witt Library as being in a collection in Grenoble). Our picture however, whilst it may derive in some way from the work sold in 2007, is a unique composition, the only example (either drawn or painted) to show just the foreground characters.
That Bruegel was a witness to the events in the composition, specifically on the Feast of the Nativity of the Baptist in 1564 (as recorded by the inscription on the Vienna drawings, probably recording one on the original), and that his prototype was either a sketch drawn from life or based on his first-hand experience, is not only possible, but also likely. The annual procession of epileptics on the Feast Day of the Nativity of Saint John the Baptist was a real historical occurrence. The type of condition seems to have been some form (or indeed maybe a number of diffferent types) of dyskinesia (it is debatable whether it was the same as the present day St. Vitus' Dance) that first appeared in the later fourteenth century in a number of mass outbreaks, of which the first was in Aachen on 24 June 1374. The association with Saint John derived from his being the Patron saint of epileptics, and his therefore being invoked for aid by sufferers and spectators; a parallel association also existed with Saint Vitus, and both names for the disease are found in early sources, although the latter's proved the more enduring. Dancers would often also be accompanied by musicians as it was believed at that the order of music could heal both body and soul (scholars such as Adam Milligan touted music as a cure for the ailments of society as well, imbuing it with the power to restrain social vices). Seizures and fits would often thus be treated by playing music in an attempt to control the erratic spasms and gyrations of the dancers.