The shores of Lough Melvin comprise part of Leitrim, Fermanagh and Donegal. The lake is about six miles long and a mile and a half at its greatest width. The castle of Rossclogher is situated on an artificial island to the south, near the Leitrim shore, and it gives its name to the Barony of Rossclogher in that county.
The Four Masters record the miraculous formation of the lake in 4694 B.C., while during the preparation of the grave of Melghe Molbhthach the waters gushed forth. He had been King of Ireland for fourteen years and was killed in battle. The lake was then called Lough Melghe, from which comes the modern Melvin.
The castle belonged to the M’Clancys, who were chiefs of Dartraigh in 1241 according to the Irish annals. They were a subordinate sept to the O’Rourkes and the name is variously spelt Glannaghie, M’Glannough, M’Glanna, M’Glanathie, M’Glanchie, Maglanshie, &c.
The lake fortress of Rossclogher was built by one of this family before the reign of Henry VIII., but the exact date is unknown.
It is interesting to note that the island next it, to the east, is called Inisheher (Inis Siar), meaning western island, having evidently received its name long before the foundations of the castle were laid, which at the present time form the most western land in the lake.
The structure upon which the fortress is built is like that of the Hag’s Castle in Lough Mask, and Cloughoghter Castle in Cavan. It consists of a foundation of heavy stones laid in the lake and filled in with smaller stones and earth so as to form an island.
The castle consists of a circular tower surrounded by a wall about five feet in height. It is built of freestone taken from the mainland near, cemented together with lime and coarse gravel. The walls, which are very thick, were coated outside with rough cast, which is unusual in the ancient buildings of the neighbourhood. On the side nearest the land are the ruins of a bastion with holes for musketry. The water is very deep between the fortress and the land, which is about 100 yards distant.
On the mainland opposite the stronghold are the remains of earthworks which would seem to have been formed by some attacking party possessing military skill. On a hill above this is situated the ancient “cattle-booley” of the MacClancy clan. It is a circular enclosure of earth, faced with stone, and is about 220 feet in circumference.