Oct. 31 is filled with religious significance.
The most obvious in the United States is Halloween, which has roots in older observances and other cultures.
Halloween became popular in the 1800s when large numbers of Irish and Scottish people immigrated to America. Halloween's earliest major root is the Celtic festival honoring Samhain, the Celtic lord of death. The Celts believed Samhain allowed dead souls to return home on the evening of the last day of their year, which was Oct. 31.
After Rome conquered the Celts, the Roman festivals of Feralia and Pomona were rolled into the day.
The significance continues through Nov. 1. The Oct. 31 evening was referred to as All Hallows’ Eve, often pronounced All Hallow E'en. Hallow comes from a word meaning holy man or saint.
In 834, All Saints’ Day, which honors all Christian saints, especially those without a feast day, was moved from the spring to Nov. 1, thus following the eve. The Mexican version is Day of the Dead.
Each of these observances brought a symbol to the current celebrations: bonfires and costumes from the Celts; apples from the Romans; and various concepts of death, including deceased ancestors visiting from the Celts and the Mexicans, and honoring the dead from the Romans.
Oct. 31 is also Reformation Day for Christians.
The Reformation marks the beginning of what became the Protestant Christian denominations.
In 1517, Martin Luther posted his “95 Theses,” which tackled the subject of indulgences, a way the church was allowing people to purchase repentance. The financial practice was used by some leaders to raise money, by allowing salesmen to market them on commission.
His document was posted at the church in Wittenburg, Germany, but the writings were made just after the invention of the printing press, so copies of Luther’s theses traveled broadly and quickly, covering Europe in two months.
Luther’s act is considered the start of the Reformation.
His intent wasn't to start a new church, but to begin a discussion and clean up what he saw as bad practices. Instead, Luther upset church leadership, lived the rest of his life as an outlaw, and started a movement picked up by many other Christians across Europe.
Sources: Dictionary of Christianity, J.C. Cooper; World Book; The HarperCollins Dictionary of Religion, Jonathon Z. Smith, editor; World Religions, John Bowker; wittenberg.de/e/seiten/thesentu.html; luther.de/e/tanschl.html; christianhistoryinstitute.org; pbs.org/empires/martinluther/cheats.html