LLANIDAN. A village situated upon the Menai Straits. The church was erected A. D. 616, and belonged, at one period, to the convent of Beddgelert, the fate of which house it shared in 1535. Edmund Downham and Peter Ashton obtained a grant of its possessions from Queen Elizabeth, but made over the same, in 1605, to Richard Prytherch, of Myfyrian, whose daughter married a Llwyd of Llugwy. The estates of this last family were purchased by the Earl of Uxbridge, who bequeathed them to his nephew, Sir William Irby, afterwards Lord Boston. Incorporated with the church wall, may be seen the famous Maen Mordhwyd, or stone of the thigh, which Giraldus mentions as possessing a locomotive property. Hugh Lupus resolved to subdue this unnatural quality by chaining it to a stone of greater weight, and casting both into the sea; but tradition asserts, that it returned to its former place, and now, at last, rests tranquil in this wall. The Romans having crossed the Menai at this place, under the conduct of Suetonius Paulinus, slew an incredible number of the islanders on a spot called Maes Mawr Gad. In the year 67, the Druids having recovered from this shock, resumed their authority, and retained it until the year 76, when the Romans, headed by Agricola, again crossed the Menai, and landing at a place called Pont-yr-Yscraphic (the Bridge of Skiffs,) a second time massacred the assembled Druids and their followers in cold blood. The fields of slaughter are known at the present day by the appellation of Llanailywynon and Bryn Lader. Tre'r Dryw is supposed to have been a dwelling-place of an arch druid, and some curious remains may be seen there. Bryn Gwyn (the Royal Tribunal), is a circular hollow, 180 feet in diameter, encompassed by a mound of earth and stones. Near this was one of the Gorseddau, or conical heaps of stone, on the summit of which the Druid sat while he delivered instruction to the people. The eminent antiquary, Henry Rowlands, was vicar of Llanidan, and is said never to have enjoyed any other literary advantages than what he discovered in his native isle. It is certain that he never travelled further than Shrewsbury from the land of his birth. He died A. D. 1723, and was interred in the church of Llanedwen. Llanidan Hall, the seat of Lord Boston, is finely situated by an arm of the sea, and commands some very fine prospects.
Source: page 1073 of Tallis's Topographical Dictionary of England and Wales, published 1860.