People don’t often think of mid-November as a month for spending lots of time outdoors. In many places, temperatures are falling, along with the first flurries of snow. The fall foliage might be dwindling, giving way to the skeletal branches of winter.

Jack-o’-lanterns, trick-or-treaters, clever costumes and spooky decorations—Halloween is one of the most beloved holidays in the United States. But where exactly did Halloween come from? What customs and folklore evolved into the festive holiday we celebrate today?