From Manx Soc vol IV,VII & IX

 APPENDIX C. [Fortresses of Magnus]

Of the fortresses of Magnus* within this isle not a vestige now remains, neither can their site be identified by oral tiadition or otherwise. From the circumstance of the Norsemen always disembarking in Jurby Parish, we should infer that they were mostly, if not wholly, in the northern parts of the Island. In the chronicle mention is made of a stronghold on an island in Mirescoge lake, in which Donald, king Harald’s friend, was confined, and this may have been one of those constructed by Magnus ; if so, lake, island, and fortress have long disappeared. In the account given of similar places in Scotland, and from the remainsof others existing in Sweden, we find they were built of logs of wood, roughly hewn and rudely put together, designed apparently more as temporary refuges than permanent places of defence. My friend Dr. Oswald, in an interesting description of an ancient encampment adjoining Kirk Braddan, suggests the possibility of its being the remains of one of the fortresses in question ; but for the reasons given above, and the very extensive nature of the ruins themselves, I am convinced it could not have been one of Magnus’s strongholds. The place described by Dr. Oswald lies between the field called the Chibber Niglus, skirting Peel road on the west and the churchyard of Braddan on the east. It consists of large stones, mounds, and irregular excavations, more or less masked, and covered by quantities of debris, the accumulation of ages. A careful examination of the spot, along with my friend, has satisfied me that it is the remains of a large Druidical temple, exactly resembling Abury. It once encompassed the entire churchyard of Braddan, and the site of old Ballafletcher House, extending as far as the Glibber Niglus. Immediately within the eastern boundary of this field, and firmly imbedded in the ground, lies a large block of stone, four feet broad by seven and a half long, and hollowed at the top like a font, which from its size, shape, and position, I infer to have been for sacrificial purposes. The inner circle of this temple is bisected by the Kewaigue road, which, with the plantation and churchyard, has completely obliterated the eastern half. The western vallum and ditch, however, is still die. tinctly to be seen, together with the stones that formed the margin of the inner enclosure. An avenue edged with stones leads from the south-west into the ditch, a peculiarity only to be found in Abury of all the Celtic monuments of Britain. Whether a second existed is difficult to say, for the whole is so defaced and altered by the growth of trees, and buildings erected within its precincts, that in a few more years its distinctive features will be entirely lost.

*According to Caradoc of Llancarran, Magnus built three fortresses in the Isle of Man