Folks , my gut feel is that the Tuatha De Danann were migrants from Hollow Earth , who settled in Ireland thousands of years ago...
A. Sutherland - AncientPages.com - Thousands of years ago, a god-like race known as Tuatha De Danann (means “children of Dana”) came to Ireland. They brought with them four magical treasures that are mentioned in early Irish literature.
The Tuatha Dé Danann as depicted in John Duncan's "Riders of the Sidhe" (1911) via Wikipedia
Tuatha De Danann is said to have come to Ireland from the north of Europe, where they had spent many years learning arts and magic. They are represented as large, strong, and beautiful beings that mingled with mortals and yet remained superior to them.
They were believed to be a race of gods or demigods with supernatural powers, human traits and personalities, and a large variety of skills in art, crafts, music, language, love, and war. There were also Druids among these people.
The 'Annals of the Four Masters' (also known as the 'Annals of the Kingdom of Ireland') describe medieval Irish history, were compiled by Franciscan monks. The story of the Tuatha De Danann, a mythical race of god-like beings with supernatural abilities, is told in these chronicles. They came to Ireland in the mists, or in a cloud, across the seas.
Myths and legends also confirm that a magical mist was produced by their arrival and it was so thick that no one was able to see their appearance. Some other versions say that they burned their ships to camouflage their arrival and thus, hide from the inhabitants of this land.
Four Magical Treasures Of Tuatha De Danann - read more
Their principal residences were Brug na Boinne, a district along the river Boyne near Stackallen Bridge in Leinster, one of the provinces situated in the east of Ireland, and the fairy-mound (sidhe = shee) of Femin in Tipperary, in the southwestern part of the country.
Each member of the Tuatha De Danann (Tuatha Dé Danann) has a special significance, skill, or capacity. Many of the tribe’s most famous characters and their qualities were mentioned in countless tales set centuries apart, and these sources showed them to be immortal.
Prominent members of the Tuatha included Dagda, a chief god, associated with fertility, agriculture, manliness, and strength, as well as magic, Druidry and wisdom; Morrígan, a goddess of war and fate; Nuada, the first king of the Tuatha De Danann; Angus (Aengus), a god of youth, beauty and love; Brigid, a fiery goddess of poetry who protects storytellers and bards; Creidne, a god of metalworking who worked with brass and bronze and forged the weapons, which the Tuatha De Danann used to battle the Fomorians.
Other prominent figures of the tribe were also Boann (wife of Dagda and mother of Angus), the Irish river goddess who gave her name to the River Boyne; Dian Cecht, a god of healing and medicine and his two children, Miach and Airmid; Goibniu, a god of metalsmithing; Manannán mac Lir, a god of the sea; Lugh, god of light, sun and crafts, and his father Cian.
Other divine personalities included Donn, god of the dead and the Otherworld; Luchta, god of the craft who helped make magical weapons for the Tuatha De Danann and Ogma, associated with eloquence and language.
The tribe is associated with two great battles of Mag Tuired. In the first of them, they fought the Fir Bolg for the ownership of Ireland and the Tuatha de Danann won this battle. The Fir Bolg people were offered the Connacht province in Ireland and the two sides lived in peace.
Giant Balor. Credit: villains.wikia.com
In the Second Battle of Mag Tuired, they confronted their traditional rivals, the Fomorians who were believed to represent the destructive or harmful powers of nature. In this military encounter, the Tuatha were also victorious; however, it was a hard battle. The Fomorian king Balor's poisonous eye, killed Nuada, the first king of the Tuatha De Danann but Balor was killed himself by his grandson, Lugh.
Balor struck down many Tuatha De Danann and he could conquer them all, but first, he had to meet his grandson, Lugh, and confront his skills with his deadly eye. Despite being half-Fomorian, Lugh fought on the side of the Tuatha De Danann and he played an important role in the Fomorians’ downfall.
For many years, the Tuatha De Danann ruled Ireland in peace until the invasion of the Milesians, a tribe of people.
The “Book of Invasions” says that the Milesians, the last mythical invaders of Ireland and the true Gaelic people of Ireland, arrived on Ireland’s shores. The Tuatha De Danann tried to fight the invaders; they even created a magical storm in an attempt to drive them away. The Milesian poet Amergin, however, calmed the sea with his invocation, and then his people landed.
"The Coming of the Sons of Miled", illustration by J. C. Leyendecker in T. W. Rolleston's Myths & Legends of the Celtic Race, 1911
The three queens of the Tuatha De Danann, (Banba, Eriu, and Fódla), gave their permission for Amergin and his people to settle in Ireland. Each of the sisters required Amergin to name the island after each of them.
The Milesian chief decided to call the island after Eriu, and two names of her two sisters were occasionally used as poetic names for Ireland. Then, the Milesians defeated the Tuatha De Danann. Amergin assigned his own people to live on the ground while the Tuatha De Danann were led underground into the ‘Sidhe’ mounds by Manannán mac Lir.
The fairy people of Irish folklore, are said to live beneath the hills and are often identified as the remnant of the ancient fabulous race of Tuatha De Danann.
The Irish myths and legends say that ‘Sidhe’ is the abode of immortals and fairy creatures. Mag Mell, is one of such places where the Tuatha De Danann are believed to live forever.