This fort of Dun Ængus, with its triple walls, and its _chevaux-de-frize_, defending it all round to the edge of the cliff, was a fortress so formidable that even still a hundred resolute men could hold it against an army, at least so long as artillery was not employed to dislodge them. Dun Conchobhair, or Conor's Fort, on the Middle Island is a still more astonishing structure, if we have regard to the time when it was built. Tradition ascribes the building of this noble fort to Conor, another son of Hua Môr, and brother of Ængus. It is larger, and better built than the Fort of Ængus, and is finely situated in the centre of the island at its highest point about 250 feet above the sea. The innermost enclosure measures 227 feet in length by 115 feet in breadth, and is oval in form. The wall had two faces and a central core; it has besides a considerable batter, and varies in different parts to from five to eight feet in width. On the east side there was a triple wall nearly eighteen feet in breadth, and twenty feet high. Its summit seems to have been approached by a flight of lateral steps in the wall, of which the traces still remain. In this, as well as in some of the other forts, are the remains of _cloghauns_, or small cells, of beehive shape, built of stone, which were evidently the habitations of the defenders of the fortress. This fact is highly important, because it goes to show, that the beehive cell of the early saints within the _caiseal_ or sacred enclosure was not a new idea, but simply the practice, which the saints had themselves seen in those pagan forts, where stone abounded. There is another fort called Mothar Dun, on the Middle Island, which is both in size and outline merely a reproduction of Dun Oonacht, to which we shall presently refer. Its largest diameter is 103 feet, and its smallest 93 feet. It was so situated on the slope of the hill, that the summit of the rocky cliff overlooks the area of the fort. Dubh Cathair, the Black Fort, is in the townland of Killeany, on Aran Mor. It was situated on an isolated promontory rising high above the sea, and separated from the mainland by a wall and fosse about 220 feet in length. The fort takes its name from the black colour of the stones with which it was built. Dun Oonacht is also on Aran Mor, at its northern extremity, and commands a magnificent view of the coast line and mountains of Connemara. In shape it is nearly circular, with a diameter of 94 feet, and is built of large stones, laid horizontally, but not in courses. The fort wall was very much broken; it has, we believe, been repaired since our visit, but it is still quite 15 feet high on the southern side. There are no traces of a _chevaux-de-frize_, as at Dun Ængus, and at the Black Fort. Dun Oghil is also in Aran Mor, and crowns the summit of the highest hill on the island. It has two concentric enclosures, the inner of which is an oval 75 by 91 feet. The name meant the Fort of the Yew Wood.