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When the Milesians—mortal humans from Iberia—arrived in Ireland, the Tuatha Dé Danann faced their first defeat. Not in battle (they could have destroyed the Milesians) but in agreement. The druids of both peoples met and negotiated. Ireland would be divided: the Milesians would have the surface world, the Tuatha Dé Danann the world below.
This was not surrender but transformation. The Tuatha Dé Danann did not leave Ireland—they sank into it. The hollow hills became their palaces. The lakes concealed their fortresses. They remained, invisible to mortal eyes except on certain nights when the boundary thinned.
This descent made them more powerful, not less. As surface-dwellers, they were vulnerable to mortal politics, aging, conflict. As Otherworld beings, they became timeless, appearing and disappearing at will, influencing mortal affairs without being bound by mortal limitations.
The sídhe (fairy mounds) were their dwelling places. Newgrange, Tara, Brú na Bóinne—each hill concealed an entrance to their realm. Mortals who entered accidentally found time flowing differently: a night in the sídhe might be a hundred years in the world above. Those who ate fairy food could never return. Those who danced with the Tuatha Dé Danann forgot their mortal names.
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