Sir James George Frazer (1854–1941).  The Golden Bough.  1922.

LXII.  The Fire-Festivals of Europe

§ 1. The Fire-festivals in general
ALL over Europe the peasants have been accustomed from time immemorial to kindle bonfires on certain days of the year, and to dance round or leap over them. Customs of this kind can be traced back on historical evidence to the Middle Ages, and their analogy to similar customs observed in antiquity goes with strong internal evidence to prove that their origin must be sought in a period long prior to the spread of Christianity. Indeed the earliest proof of their observance in Northern Europe is furnished by the attempts made by Christian synods in the eighth century to put them down as heathenish rites. Not uncommonly effigies are burned in these fires, or a pretence is made of burning a living person in them; and there are grounds for believing that anciently human beings were actually burned on these occasions. A brief view of the customs in question will bring out the traces of human sacrifice, and will serve at the same time to throw light on their meaning.   1
  The seasons of the year when these bonfires are most commonly lit are spring and midsummer; but in some places they are kindled also at the end of autumn or during the course of the winter, particularly on Hallow E’en (the thirty-first of October), Christmas Day, and the Eve of Twelfth Day. Space forbids me to describe all these festivals at length; a few specimens must serve to illustrate their general character. We shall begin with the fire-festivals of spring, which usually fall on the first Sunday of Lent (Quadragesima or Invocavit), Easter Eve, and May Day.   2