On Beltane eve the Celts would build two large fires, Bel Fires, lit from the nine sacred woods.

Traditionally, sacred woods kindled by spark from flint or by friction -- in Irish Gaelic, the Beltane Fire has been called teine eigin (fire from rubbing sticks). * Jump over the Beltane Fire, move through it, or dance clockwise around it. * Livestock was driven through it or between two fires for purification and fertility blessings. * In ancient times Druid priests kindled it at sacred places; later times, Christian priests kindled it in fields near the church after performing a Christian church service. * Rowan twigs were carried around the fire three times, then hung over hearths to bless homes. * In the past, Beltane community fire purification customs included symbolic sacrifice of effigy knobs on the Beltane Cake (of barley) to the fire, or, in medieval times, mock sacrifice of Beltane Carline (Hag) who received blackened piece of Beltane Cake; Maypoles in Spain were each topped with a male effigy which was later burned.

The herds were ritually driven between two needfires (fein cigin), built on a knoll. The herds were driven through to purify, bring luck and protect them as well as to insure their fertility before they were taken to summer grazing lands. An old Gaelic adage: "Eadar da theine Bhealltuinn" - "Between two Beltane fires".

The old Celtic name for May Day is Beltane (in its most popular
Anglicized form), which is derived from the Irish Gaelic 'Bealtaine'
or the Scottish Gaelic 'Bealtuinn', meaning 'Bel-fire', the fire of
the Celtic god of light (Bel, Beli or Belinus). He, in turn, may be
traced to the Middle Eastern god Baal.

Other names for May Day include: Cetsamhain ('opposite Samhain'),
Walpurgisnacht (in Germany), and Roodmas (the medieval Church's name).
This last came from Church Fathers who were hoping to shift the common
people's allegiance from the Maypole (Pagan lingham - symbol of life)
to the Holy Rood (the Cross - Roman instrument of death).

In ancient Ireland there was a Sacred Tree named Bile, which was the center of the clan, or Tuatha. As the Irish Tree of Life, the Bile Pole, represents the connection between the people and the three worlds of Bith: The Skyworld (heavens), The Middleworld (our world), and The Otherworld. Although no longer the center life, the Bile pole has survived as the Beltane Maypole.

Just thought I would include the last one too. It is nice to know.