St. John's Eve, St. Mark's Eve
and Allhallow Even, are times when poets say the forms of all such persons as are about to die in the ensuing twelve months make their solemn entry into the churches of their respective parishes. On these eves all sorts of goblins are about. Brand says, “On the Eve of John the Baptist's nativity bonfires are made to purify the air” (vol. i. p. 305).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894