Lugnasad (in Old Irish; Modern Irish Lúnasa or Lughnasa); Modern Scottish Gaelic Lùnasdal; pronounced loog nas a, roughly), generally celebrated by Neo Pagans on August 1, is the Irish festival that celebrates the beginning of the harvest. The festival is still kept as a secular national festival in a number of European nations that were once settled by the ancient Celts, but today, it's largely a Neo Pagan feast. Etymologically, the feast seems to be closely associated with the Irish deity Lug Lámfada, better known in English texts as Lugh, cognate with the Gaulish deity Lugos, the inspiration for the Celtic names of the cities of Lugdunum" (or "Lugodunon" in Gaulish), literally Lugh's (Lug) fortress (dunos or dunon), better known as Lyons, the city in Gaulish France that Caesar says had a yearly festival in celebration of the Emperor Augustus, a festival that seems to have been extant as a tribal feast.
Lugnasad is the start of the harvest season, particularly the ripening of grain and masts (nuts). It was according to ancient Irish law texts a propitious time for couples to join with an option to formalize the union if, on the contractual year-and-a-day later, they wished a more permanent relationship. In more modern folklore, a "Teltown marriage" enacted at Lugnasad could be dissolved before the year and a day term if the couple stood back to back before witnesses, and walked away from each other, one going south, and one going north.
Irish mythological texts, specifically, Lebor Gabala Eirenn, the Book of the Takings of Ireland, assert that Lugnasad was established by Lugh in honor of his foster mother Tailtiu, who, like Lug's real mother Eithne, was one of the Fomoire. Depending on the text, and the version of the Irish myth you check, Tailtiu was the queen of Eochaid mac Eirc, the last Fir Bolg King of Ireland, who named his capital after her, and the daughter of the king of Spain. Alternatively, Tailtiu was the daughter of Mag Mór or "Great Plain" (which implies some sort of connection to the earth itself). Either way, Tailtiu is said to have died in the aftermath of Cath Maige Tuired, after clearing the plain of Breg in County Meath so that it could be farmed.
Tailtiu's foster son Lugh established a feast in her honer at Tailtiu, modern Teltown, in Meath, between Navan and Kells. In her honor, an annual festival or oenach was held. The festival included funeral games, like hurling, gambling, horse racing, and displays of martial arts. And beer. The Lebor Gabala says that the festival was held fifteen days before and terminated fifteen days after August 1. This is a typical way of noting the duration of the four major oenachs and festivals.
The historical record suggests that there were games on Lugnasad as late as the 1770s. Moreover, Tailtiu was where the principal assembly of the early Uí Néill dynasties was held, making the site important in terms of kingship and ritual. Other events at Tailtiu include the victory of the Milesians, the Sons of Mil over the Tuatha Dé Danann, the deaths of Banba, Ériu, and Fódla and the resting place of the warriors of the Ulaid. For those interested in the customs and relevance of Lugnasad, see The festival of Lugnasad. Máire MacNeil (Oxford University Press, 1962).