5th of November:

 The tradition of Guy Fawkes-related bonfires actually began the very same year as the failed coup. The Plot was foiled in the night between the 4th and 5th of November 1605. Already on the 5th, agitated Londoners who knew little more than that their King had been saved, joyfully lit bonfires in thanksgiving. As years progressed, however, the ritual became more elaborate.