Samhain (pronounced "sah-vihn") was an Irish post-harvest festival which lasted three days, and involved great bonfires in a knowingly futile attempt to keep the sun from "going to sleep." Ireland is far enough north that by the end of October, beginning of November, the days are getting really, really short. The Irish, most of whom throughout history would probably have loved to have seen some Catholics blow-up Parliament, nevertheless "celebrate" Guy Fawkes Day (November 5?), and one of the prominent features of their version of it is bonfires in the streets.
It is said that many of our Hallowe'en customs come from the rites of Samhain. The early Christian missionaries associated the feast with All Souls Day (October 31) to wean the "pagans" away from their practices and get them to come on board. All Souls Day is followed by All Saints Day (November 1), which, in an older form of English was All Hallows (i.e., Saints) Day, so that October 31 is All Hallows Eve--Hallowe'en (a shortening of Hallows Even[-ing]).