When is Halloween ?

Halloween is on October 31st every year. Why October 31st? Because Halloween has its origin in an ancient, pre-Christian, end-of-year festival that was celebrated by the ancient Celtic people who lived in Scotland as well as the ancient Anglo-Saxon people who lived in Britain. This festival was known as the Samhain or Sambain or Saman festival ["Summer's End" in Gaelic; pronounced either as "Sah-win" or "Sah-van" or ""Sow-in" (where "ow" rhymes with "cow")", depending on the interpretation], in which it was believed that on the day of November 1st, the Celtic Lord of Death - known as Samhain or Sambain or Saman - called together all the souls who were wicked and who died over the past year. The Druids, who were the religious leaders of the Celtic people, were an order of priests (who also served as teachers) who practised the customs of the Samhain or Sambain or Saman festival, believed that on the eve of the festival, the evening of October 31st, various spirits of the dead, including ghosts, demons, elves, fairies, hobgoblins, and witches (who sometimes took the shape of black cats), rose from their graves to fly around and essentially roam the earth in search of revisiting their homes. The Druids also believed that in the evening on October 31st, all the witches would gather together to worship the devil. Many of the associated pagan customs of the Samhain or Sambain or Saman festival, which were centered around the themes of death, reawakening souls, and evil spirits, were incorporated into a holy feast day by the Roman Catholic Church in the 9th century A.D. that honored all known and unknown saints. This day was known as All Saints' Day and was originally observed on May 13th (on May 13, 609 A.D., the first All Saints' Day was observed when Pope Boniface IV accepted the Pantheon as a gift from the Emperor Phocas), but Pope Gregory IV (ruled as pope from 827 A.D. - 844 A.D.) wanted to make it easier for the pagans to integrate into the church, and so in either 834 A.D., 835 A.D., 837 A.D., or 844 A.D. (according to various scholars), All Saints' Day was transferred to November 1st to coincide with the Samhain festival, with the eve of All Saints' Day being observed in the evening on October 31st along with the associated pagan customs. In medieval England, All Saints' Day was known as All Hallows' Day and the eve of All Saints' Day was known as All Hallows' Eve. Over time, All Hallows' Eve became a secular observance with secular customs and the name Halloween was eventually contracted out of the name All Hallows' Eve and used to denote the evening of the day of October 31st. Associated secularized customs surrounding Halloween, most which derived from secularizing ancient Celtic and Anglo-Saxon customs of the Druids, or priests (who were also teachers), that were practised on the festival of Samhain or Sambain or Saman, and some which grew out of adapting these secularized Scottish, Irish, and English Halloween customs in the United States, account for the reasons why Halloween is celebrated on October 31st of every year as well as why the associated Halloween customs are observed in the evening on this day.