A number of stone circles and dolmens, including for example, Avebury, exhibit a west-south-west alignment, the azimuth angle of the setting sun on 31st October.

The early literature says Samhain was marked by great gatherings and feasts and was when the ancient burial mounds were open, which were seen as portals to the Otherworld.

[3] Like Bealtaine, Samhain was a liminal or threshold festival, when the boundary between this world and the Otherworld blurred, making contact with the aos sí (the 'spirits' or 'fairies') more likely.

Mumming and guising were part of the festival from at least the early modern era, whereby people went door-to-door in costume, reciting verses in exchange for food.

The name of the superficially similar Galician festival of Samaín from the Cedeira comarca is etymologically unrelated, being derived from Latin sambucum 'elderberry'.

[18] More recently, linguists Xavier Delamarre and Ranko Matasović have proposed that it derives from proto-Celtic *samoni ('reunion, assembly'), cognate with Old Norse saman, Gothic samana and Sanskrit samāná (all meaning 'together'), as well as the Old Irish term bech-samain ('bee swarm').

[20] The word Samain is believed to be related to the month name SAMON on the Gaulish Coligny calendar from the 2nd century CE.

Sir James George Frazer, in his 1890 book, The Golden Bough: A Study in Magic and Religion, theorized that these festivals, particularly 1 May and 1 November, were significant to herding communities practicing seasonal transhumance.

[36] Each year the fire-breather Aillen emerges from the Otherworld and burns down the palace of Tara during the Samhain festival after lulling everyone to sleep with his music.

One Samhain, the young Fionn mac Cumhaill, stays awake and slays Aillen with a magical spear, for which he is made leader of the fianna.

In a similar tale, one Samhain, the Otherworld being Cúldubh emerges from the burial mound on Slievenamon and snatches a roast pig.

[37] Acallam na Senórach ('Colloquy of the Elders') tells how three female werewolves emerge from the cave of Cruachan (an Otherworld portal) each Samhain and kill livestock.

In the Lebor Gabála Érenn (or 'Book of Invasions'), each Samhain the people of Nemed had to give two-thirds of their children, their corn, and their milk to the monstrous Fomorians.

[39][40] This tribute paid by Nemed's people may represent a "sacrifice offered at the beginning of winter, when the powers of darkness and blight are in the ascendant".

[41] According to the later Dindsenchas and the Annals of the Four Masters—which were written by Christian monks—Samhain in ancient Ireland was associated with a god or idol called Crom Cruach.

[43] The Boyhood Deeds of Fionn tells how each Samhain the men of Ireland went to woo a beautiful maiden who lives in the fairy mound on Brí Éile (Croghan Hill).

[44] Some academics suggest that these tales recall human sacrifice,[45] and argue that several ancient Irish bog bodies (such as Old Croghan Man) appear to have been kings who were ritually killed,[46] some of them around the time of Samhain.

[47] In the Echtra Neraí ('The Adventure of Nera'), King Ailill of Connacht sets his retinue a test of bravery on Samhain night.

The invasion of Ulster that makes up the main action of the Táin Bó Cúailnge ('Cattle Raid of Cooley') begins on Samhain.

[55] In The Stations of the Sun: A History of the Ritual Year in Britain (1996), Ronald Hutton writes: "No doubt there were [pagan] religious observances as well, but none of the tales ever portrays any".

[57] It is mentioned in Geoffrey Keating's Foras Feasa ar Éirinn, which was written in the early 1600s but drew on earlier medieval sources, some of which are unknown.

He claims that the feis of Tara was held for a week every third Samhain when the nobles and ollams of Ireland met to lay down and renew the laws, and to feast.

[62] It is suggested that the fires were a kind of imitative or sympathetic magic; mimicking the Sun, helping the "powers of growth" and holding back the decay and darkness of winter.

One man would wade into the water up to his waist, where he would pour out a cup of ale and ask 'Seonaidh' ('Shoney'), whom he called "god of the sea", to bestow on them a good catch.

[3][85] The belief that the souls of the dead return home on one night of the year and must be appeased seems to have ancient origins and is found in many cultures throughout the world.

[86] James Frazer suggests, "It was perhaps a natural thought that the approach of winter should drive the poor, shivering, hungry ghosts from the bare fields and the leafless woodlands to the shelter of the cottage".

[90] In Scotland, young men went house-to-house with masked, veiled, painted, or blackened faces,[62][94] often threatening to do mischief if they were not welcomed.

Charles Vallancey wrote that they demanded this in the name of St Colm Cille, asking people to "lay aside the fatted calf, and to bring forth the black sheep".

[citation needed] The "traditional illumination for guisers or pranksters abroad on the night in some places was provided by turnips or mangel wurzels, hollowed out to act as lanterns and often carved with grotesque faces".

[123][124][125][126] Some Neopagans celebrate it at the astronomical midpoint between the autumnal equinox and winter solstice (or the full moon nearest this point), which is usually around 6 or 7 November in the Northern hemisphere.