A great stone fort dating from perhaps early Christian times at Inishowen Head in north-east Co. Donegal, 5 miles W of [London]Derry, on the western entrance to Lough Foyle. Although the word grianán [sun porch] has an early association with the site, the structure is clearly not a sun porch; the names Grianán of Ailech and Greenan Elly are romantic attributions from the 19th century. In the Old Irish Lebor Gabála [Book of Invasions], it is Ailech Néit; also Aileach Ned. ‘Capital’ of Ulster after the destruction of Emain Macha, Aileach was once the equal of Tara, Cashel, Cruachain, or Naas. Standing on a high (803 feet) promontory, the ring fort commands one of the most spectacular panoramic views to be had from any man-made structure in the British Isles.
By tradition it was built by the Tuatha Dé Danann and became one of their most important fortresses. When Ith the Milesian spy came to examine the country, he was slain by warriors who came from Aileach. The architect and stonemason of the fortress was Ringin. In some stories the fortress is thought to be occupied by Frigriun mac Rubai Ruaid and is called Aileach Frigrenn. According to some traditions Nuadu Airgetlám is buried here. In Irish history Aileach became the seat of the Uí Néill, when Eógan (1), son of Niall Noígiallach [of the Nine Hostages], seized it c.425; his line continued until c.1200. The actual date of the current structure is unknown; materials from some early monument were ‘reconstructed’ by Dr Bernard of Derry c.1870.