The fortress of Aileach is nearly a hundred feet in diameter in the inside. It is not known if it was ever roofed, but it is probable that it was. There were two lines of earthen ramparts round it, but they have nearly disappeared. John O'Donovan thought that the entire hill of Grianan, on which the fortress stands, was once enclosed by a vast rampart of earth, and that cultivation has destroyed all but the faintest traces of it. It seems probable that Aileach was intended more for a stronghold than for a permanent dwelling-place. It may have been inhabited only when a siege or an invasion was expected. One of its names, or rather the first part of one of its names, "Grianan," would indicate that it was intended only as a summer residence, like the Dunsinane = _Dún soinine_, fine weather fortress, of Macbeth. Those who could live in winter on top of the wind-swept hill on which Aileach stands without getting coughs or colds would require constitutions of iron and lungs of brass. O'Donovan says that if any reliance can be placed on Irish chronology, the antiquity of Aileach must be very great, no less than upwards of a thousand years before the Christian era. He says, also, that the poet, part of whose poem on Aileach is given below, in making the Tuata de Danaan King, Eochy, generally known in Irish history and legend as the Dagda, contemporaneous with the Assyrian King, Darcylus, exactly agrees with the chronology of O'Flaherty and Usher, who say that he reigned 1053 years before the Christian era. There is a poem in the "Book of Lecan" on Aileach by the poet to whom O'Donovan alludes, that in language and _tournure_ bears the marks of extreme antiquity. Even O'Donovan, great a Celtic scholar as he was, had apparently extreme difficulty in translating it. It has never been published. The first dozen or so lines are given here:-- "Aileach Fridreann, arena of mighty kings. A _dun_ through which ran roads under heroes through five ramparts. Hill on which slept the Dagda. Red its flowers. Many its houses. Just its spoils. Few its stones. A lofty castle is Aileach. Fort of the great man. A sheltering _dun_ over the lime [white] schools. A delightful spot is Aileach. Green its bushes. The sod where the Dagda found the mound wherein rested Hugh."