Samhain + All Saints’ Day = Halloween

How the pagan Irish festival of Samhain merged with the Catholic festival of All Saints’ Day to become today’s secular Halloween

Samhain

Samhain is a Gaelic festival marking the end of the harvest season and the beginning of winter or the "darker half" of the year. Traditionally, Samhain is celebrated from sunset on 31 October to sunset on 1 November, which is about halfway between the autumn equinox and the winter solstice. It is one of the four Gaelic seasonal festivals, along with Imbolc, Beltane and Lughnasadh. Historically, it was widely observed throughout Ireland, Scotland and the Isle of Man.  Samhain is believed to have pagan origins and there is evidence it has been an important date since ancient times.

In the 9th century AD, Western Christianity shifted the date of All Saints' Day to 1 November, while 2 November later became All Souls' Day. Over time, Samhain and All Saints'/All Souls' merged to create the modern Halloween.[5] Historians have used the name 'Samhain' to refer to Gaelic 'Halloween' customs up until the 19th century.[6]

Since the latter 20th century, Celtic neopagans and Wiccans have observed Samhain, or something based on it, as a religious holiday.[7] Neopagans in the Southern Hemisphere often celebrate Samhain at the other end of the year (about 1 May).

All Saints' Day

The Roman Catholic holy day of All Saints (or All Hallows) was introduced in the year 609, but was originally celebrated on 13 May.^[65] In 835, Louis the Pious switched it to 1 November in the Carolingian Empire, at the behest of Pope Gregory IV.^[65] However, from the testimony of Pseudo-Bede, it is known that churches in what are now England and Germany were already celebrating All Saints on 1 November at the beginning of the 8th century.^[65][66][67] Thus, Louis merely made official the custom of celebrating it on 1 November. James Frazer suggests that 1 November was chosen because it was the date of the Celtic festival of the dead (Samhain) – the Celts had influenced their English neighbours, and English missionaries had influenced the Germans. However, Ronald Hutton points out that, according to Óengus of Tallaght (d. ca. 824), the 7th/8th century church in Ireland celebrated All Saints on 20 April. He suggests that the 1 November date was a Germanic rather than a Celtic idea.^[65]

Over time, the night of 31 October came to be called All Hallows' Eve (or All Hallows' Even). Samhain influenced All Hallows' Eve and vice versa, and the two eventually morphed into the secular holiday known as Halloween.