According to Tony Nugent, the Grianan was also used as a Mass rock during the anti-Catholic religious persecution that began under Henry VIII and ended only with Catholic Emancipation in 1829.

The eastern ascent of the hill is described as gradual but within 30 metres (98 ft) of the top, it terminated in a circular apex.

The ramparts that remained were made of earth and stone and follow the natural form of the hill with an irregular circular pattern.

The most interesting stone object was "a slab of sandstone, chequered into thirty-six squares", which Lacy believed to be some kind of gaming board.

The height from the best surviving walls were given as approximately 6 ft, whilst having an obvious batter, and sloping inwards like Staigue Fort in Kerry.

He also puts forward the idea that a circular form was favoured because corners could act as a dwelling-place of evil spirits.

The only exception to this are the ringforts built in areas of bad drainage where high places are the only suitable spots for habitation.

Raftery names three monuments which he finds hard to categorise as being either a ringfort or a hillfort: Cahirciveen; Carraig Aille; and Lough Gur.

Hillfort consist of 'large hilltop areas on which the summit is enclosed by one (univallate) or multiple ramparts (multivallate) of earth or stone'.

Its defensive nature is explicit due to the system of stone slabs, known as chevaux de frise, planted into the ground outside the fort structure itself.

Stout gives several examples to indicate their symbolic importance simply due to their impracticality as defensive structures.

[citation needed] Lacy suggests that the innovative nature of the stone fort of Aileach must have been an unusual site when it was first constructed.

Finds from ringforts typically include items which date from the second half of the first millennium: a hand-made, bucket shaped pottery style called 'Souterrain Ware', which uses local clays and can be decorated or undecorated; glass beads; bone, bronze and iron pins; and artefacts of bone and metalwork.

After the decisive battle of Cloítech in 789, when the Cenél nEógain won total control of the over-kingdom of the northern Uí Néill, the successful kings relocated to the Grianán, building it inside the pre-existing prehistoric hillfort as a visual symbol of their new mastery of all the landscape visible from that commanding view.

Multivallate hillforts are suggested to be confined to the West and South of the country; univallate forts are to be found in the north and east.

Ringforts are rarely found in similarly elevated areas of Londonderry and Tyrone, including the Sperrin Mountains and west of the Roe River.

Although some Early Christian settlement is present, the areas as a whole was relatively sparsely settled with ringforts despite the Mourne and Foyle river valleys being extremely suitable for agricultural exploitation.

She identified 124 ringforts in an area reaching from Glen Head to Lough Ekse and south along the county boundary to Bundoran.

Brown earth and grey-brown podzolic soils were particularly favoured explaining the concentration of sites west of Donegal Bay.

[citation needed] Theories accounting for the function of hillforts range from their use as defensive sites to ceremonial enclosures.

A number of writers in the nineteenth century suggested that one of the two sites marked as Regia (or royal place) on Ptolemy's map of Ireland, may be identified with the Grianán.

Both Petrie and Lacy suggest that it comes from an adjective derived from old Irish "Ail", which means a rock, stone or boulder.

In the historic period, from the middle of the sixth century, the Grianán of Aileach is always thought of as the capital of the northern Ui Neill, the dynasty descended from Niall of the Nine Hostages.

Circular houses, which are directly associated with the main phase of ringfort occupation, tended to be located towards the centre of the enclosure placing them furthest from an outside attack.

In Irish mythology and folklore, the ringfort is said to have been originally built by the Dagda, a god and the celebrated king of the Tuatha Dé Danann, who planned and fought the battle of the second or northern Magh Tuireadh, against the Fomorians.

The history of the death of Aedh, and the building of Aileach, is given at length in a poem preserved in the Book of Lecan which has been printed with an English translation (verse 38 Ordnance Memoir of the parish of Templemore, Dr Perie).

The building of Aileach's fastness came to an end, Though it was a laborious process; The top of the house of the groaning hostages "One stone closed".

Here Frigrind built a splendid house of wood for his wife from red yew, carved and emblazoned with gold and bronze; thick set it with shining gems.

Also worth noticing is the fact that Aileach is one of the few spots in Ireland that is marked in its proper place by the geographer Ptolemy of Alexandria, who some say lived in the second century, nearly two hundred years before the time of Frigrind.

[7] The fort appears in video games such as Total War: Thrones of Britannia and the Wrath of the Druids DLC expansion for Assassin's Creed Valhalla.