The Castle of Holy Island stands on a steep rock, about half a mile to the eastward of the Abbey. It is wholly inaccessible, except by a winding pass cut through the rock on the south side. The date of its foundation is unknown; but it is supposed to have been first built by the monks, as a place of refuge against the piratical attacks of the Danes, who frequently annoyed them, and twice burnt their abbey. The most memorable event in the meagre history of this castle is its capture for the Pretender, by two men, Launcelot Errington, and his nephew Mark, in 1715. The garrison at that time consisted of a sergeant, a corporal, and ten or twelve men. Errington, who was master of a little vessel then lying in the harbour, invited the sergeant, and such of his men as were not on duty, to drink with him on board of his ship. The invitation being accepted, he plied them so well with brandy as to render them incapable of opposition. Framing an excuse for going ashore, he proceeded to the castle with his nephew, and succeeded in turning out the old gunner, the corporal, and two soldiers, being all that were on duty. He then shut the gates, and hoisted the Pretender's colours, but being disappointed in the succour which he expected, and a party of the king's troops arriving from Berwick, he and his nephew made their escape over the castle walls, and endeavoured to conceal themselves among the rocks and sea-weed, to the south-eastward of the castle till it was dark, when they intended to swim to the mainland. In consequence of the rising of the tide, they were obliged to swim while it was yet light, and, being perceived by the soldiers, they were taken, and conveyed to Berwick gaol, from which, however, they broke out before they were brought to trial, and escaped to France. On the suppression of the rebellion they took the benefit of the general pardon, and returned to England. Holy Island is of an irregular form. Its greatest length, including a low sandy point, which stretches out towards the west-north-west, is about two and a half miles. Its mean breadth does not exceed a mile and a half. Holy Island harbour is a small bay or haven on the south side of the island, between the castle and the ruins of the monastery. On the bar, which is about a mile distant from the town, there is about nine feet at low water at spring-tides. The flood then sets with a strong current in the channel between the island and the mainland; and at high-water there is twenty-four feet on the bar. There is no lighthouse on Holy Island, but there is a beacon on the "Heugh"--a hill between the town and the harbour--on which, in bad weather, when pilots cannot get off, a flag is hoisted during the time of tide that ships may safely enter. In gales of wind from the eastward, coasting vessels sometimes seek shelter in Holy Island harbour, and find good anchorage before the town in three fathoms at low-water.