They were the powers of light and warmth, and did battle with the Fomhoire, or powers of night and death and cold.  

According to the Lebor Gabala, the book of invasion, the Tuatha De Danann came to Ireland in obscure clouds, landing on a mountain in the west.  From the same book we learn that these gods were capable of causing an eclipse which lasted for three days.  They came from the northern isles of the world, learning lore and magic and craft and wizardry and cunning, until they surpassed the sages of the arts of heathenism.

There were four cities in which they learned lore and science and diabolic arts, to wit, Falias and Gorias, Murias and Findias.  Out of Falias was brought the Stone of Destiny, or Lia Fail which was in Tara.  In used to roar under every king that would take the realm of Ireland.  Out of Gorias was brought the Spear that Lugh had.  No battle was ever won against it or him who held it in his hand.  Out of Findias was brought the Sword of Nuadhu.  When it was drawn from its deadly sheath, no one ever escaped from it, and it was irresistible.  Out of Murias was brought Dagdha's Cauldron.  No company ever went from it unthankful.

At the time of the arrival of the Tuatha Dé Danann the race inhabiting Eire was known as the "fir Bolgs" who were divided into three tribes.The "fir Domnann" controlled North Munster, South Munster and Connaught. The "Fir Bolg" controlled Ulster and the "Fir Gaillon" Leincester. At that time their king was called Eochid son of Erc.  

It is said that the Tuatha Dé Danann arrived on the 1st of May (Beltaine) bringing with them treasures from their home cities.  The gods reached the coast of Ireland in a shrowd of mist to conceal
themselves from the Fir Bolgs. Morrigu and her fellow war godesses created fogs, rainstorms and larva to fall on the Fur Bolgs so that they had to take shelter for three days until their own druids overcame the enchantments.  Finally the two sides met and after a period of truce the two sides began a bloody battle where Eochid was slain and the Fir Bolgs defeated. It was in this very battle that Nuada had his hand sliced clean off and, although Diancecht skillfully made him a
hand of silver, he was sufficiently disfigured to have to give up the rule of the Tuatha Dé Danann.
And so it was that the Tuatha Dé Danann took control of Ireland. The surviving Fir Bolgs were given Connaught to live in and to this day there are those that claim ancestory to that ancient tribe.

The Tuatha De Danann had many powerful Gods, such as Diancecht, the God of Medicine; The Dagda (The Good God) who specialized in Druidic Arts; Goibhniu who knew Smithing; Lugh, a God of Arts and Crafts, and Oghma, the God of Communications.

When the Milesians (a Celtic tribe from Spain) came upon the island, there was a third great battle.  Three of the Tuatha De Danann were sent in advance to stop the Milesians, namely Banbha, Fodhla and finally Eriu.  Each of them failed and a great battle ensued.

After the Tuatha De Danann had been defeated by the Milesians, the first human ancestors of the Irish people led by the Sons of Mil, the Lebor Gabala gives no further details of the Tuatha De Danann except to say that an agreement was reached between them that the gaelic people would live on the upper half of the ground and that the Tuatha De Danann would live in the Otherworld - they retreat to Tir na nOg.

Those that chose to stay in Ireland became the Irish Sidhe, a spirit race of faeries. Finvarra was High King of the Daoine Sidhe, and thought to be King of the Dead, still holds court in the Hill of Knockma.
Great masters of magick; whom were said to come from the stars to teach earth's children about love and harmony. They were the Faery people, who of great warriors served the Ard Righ, or High King, whose palace was Tara. Many moved on to be Fenian Heroes.

Tir na nOg (pronounced "Tyeer-nahn-ohgg" - Land of Youth) is where the Irish faeries known as Tuatha De Danann fled. In this magical place they spend their days feasting, gaming, love-making and partaking in beautiful music.  The faeries can even enjoy the thrill of battle, for anyone slain is resurrected the following day.  It is the paradise that mortals can only dream of.

To learn more about the historical Tuatha De Danann, and the gods and goddesses of ancient Ireland, click on one or more of these links: