Topographical Dictionary of Scotland, Samuel Lewis - 1851
MOUSA, an island, in the former quoad sacra parish of Sandwick-and-Cunningsburgh, parish of Dunrossness, county of Shetland j containing 12 inhabitants. This island lies close to the east coast of the Mainland, and at the entrance of Aith's Voe; it is also called Queen's Isle, and is about a mile in length and three quarters of a mile in breadth. The village of Cunningsburgh is distant from it, north-westward, about two miles. In this island is a most perfect specimen of an ancient Scandinavian fortress, or, as some call it, Pictish castle. It is nearly entire, and in .shape resembles a dice-box: its height is about forty-two feet, and, over the walls, its diameter fifty feet; the walls are about ten feet in thickness, and hollow in the middle. The fort stands on the shore, and seems to have been a place of defence. Opposite to it are the ruins of another castle of the same description, round which are still visible the sites of a number of small houses.