The Grianan of Aileach ( ; ), sometimes anglicised as Greenan Ely or Greenan Fort, is a hillfort atop the high Greenan Mountain at Inishowen in County Donegal, Ireland. The main structure is a stone ringfort, thought to have been built by the Northern Uí Néill, in the sixth or seventh century CE; although there is evidence that the site had been in use before the fort was built. It has been identified as the seat of the Kingdom of Ailech and one of the royal sites of Gaelic Ireland. The wall is about thick and high. Inside it has three terraces, which are linked by steps, and two long passages within it. Originally, there would have been buildings inside the ringfort. Just outside it are the remains of a well and a tumulus.
By the 12th century, the Kingdom of Ailech had become embattled and lost a fair amount of territory to the invading Normans. According to Irish literature, the ringfort was mostly destroyed by Muirchertach Ua Briain, King of Munster, in 1101. Substantial restoration work was carried out in 1870. Today, the site is protected as a national monument and is a tourist attraction.
Description and interpretation
The Grianán is located on the western edge of a small group of hills that lie between the upper reaches of Lough Swilly and Lough Foyle. Although the hill is comparatively not that high, the summit dominates the neighbouring counties of Londonderry, Donegal and Tyrone. Located at the edge of the Inishowen peninsula, it is northwest of the ecclesiastical site of Derry. The histories of the sites are closely linked. There is much legend and historical material related to the Grianán of Aileach. The Irish annals record its destruction in 1101. The main monument on the hill is a stone cashel, restored in the nineteenth century, but probably built in the eighth century CE. The summit's use as an area of settlement may go back much further. A tumulus at the Grianán may date back to the Neolithic age. A covered well was found near the cashel in the early nineteenth century.
Irish antiquarian George Petrie first surveyed the Grianán of Aileach in the 1830s. At this time the cashel was nothing more than a mere ruin. He gives a description of the hill and the monument. The eastern ascent of the hill is described as gradual but within of the top, it terminated in a circular apex. An ancient road between two ledges of natural rock led to the summit. The cashel was surrounded by three concentric ramparts. Petrie suggests that, in the fashion of other monuments of this type such as Emania, the whole hill may have been enclosed by many other ramparts. There is no physical or historical evidence for this. The ramparts that remained were made of earth and stone and follow the natural form of the hill with an irregular circular pattern. They ascend above each other creating levelled terraces. The circular apex of the hill within the outermost enclosure contains about , within the second about and within the third about . Currently, the innermost bank is very low, worn and heather-covered but traceable for almost its entire circuit. The other two banks are in a similar state but are untraceable for long sections. Between the inner most rampart and the cashel, the road dwindles in its width and curves slightly to the right. This "path" was strengthened on either side by walls. At the time of the survey only the foundation stones of these walls remained. Petrie's plan of the site shows a line of stones leading up to the entrance. These are now gone.
The ruins of the cashel itself are described as being a circular wall enclosing an area of in diameter. The wall had a height of with a breadth varying from to . While not perpendicular, it had an inclination inwards indicating its similarity to most other Irish stone forts. Petrie suggests that it was probably originally between twice and four times as high as it was when he surveyed it. up on the interior side of the wall, the thickness was due to the presence of terracing. The terrace is reached by flights of steps on either side of the entrance gateway. Fallen stones had covered any other existing stairs. Petrie suggests that there were originally three or four such terraces ascending to the top of the wall. On each side of the entranceway, there are "galleries" within the wall. Their precise purpose is not clear and they do not connect with the entrance. These two wall-passages, one on the south and another from the northeast run towards the gateway, but stop short. Near the north end of the south passage is a small recess in its west wall. At the south end of the north passage there is a seat-stone.