Situated three and a half miles north by east of Newcastle, County Down, this donjon fortress commands an extensive view of Dundrum Bay and the surrounding district of Lecale. The castle was built on the site of an older fortification known as Dun Rudhraidhe, or Rury’s Fort, which is said to have been the scene of the great feast given by Bricrin of the Poisoned Tongue, to King Connor MacNessa and the Red Branch Knights at which he induced them to make war on one another, as is chronicled in “The Book of the Dun Cow.” The present village of Dundrum (Dundroma, signifying the fort on the ridge) lies between the castle and the shore, while to the east of the fortress are the ruins of an Elizabethan mansion erected by a former owner of the castle.

The circular keep or donjon is built upon a rock, and has an external diameter of some 45 feet, the walls of which are 8 feet thick above the projecting base. The tower at present stands about 50 feet in height. The cellar below is hewn out of the rock on which the building was erected, and is said at one time to have contained 200 tuns of Spanish wine belonging to O’Neill.

To the east of the entrance is a circular newel stair 3 feet 3 inches in diameter, constructed in the thickness of the wall and leading to the parapet. From this there are openings at each storey, and it is most likely from the position of the offsets in the wall that the floors were of wood supported on beams, the holes for the latter being still visible at different levels.

Round this tower was the courtyard or bawn, encircled by a high wall 4 and 5 feet thick, which was again protected by a fosse or moat, still to be seen on the north and west sides. The bawn was occupied by the buildings for the retainers, and perhaps the family in times of peace, and is of a roughly circular form about 150 feet across.

South-east of the donjon, in the line of wall, are the two ruined towers which protected the barbican gate, the corbel blocks of which still remain over the archway, and originally supported the defences of the gateway. From these, numerous rebels were hanged in the rebellion of 1798.

The castle was built of stone quarried to form the fosse, mixed with land stones of the district. Little has been done to alter the twelfth or thirteenth century architecture, except the opening out of windows. On the side of the ruined manor the outer fortifications would seem to have been levelled to make terraced gardens to the later dwelling.

It is generally supposed that Dundrum Castle was built by John de Courcy at the end of the twelfth century for the Knights Templars, after his daring conquest of Ulster in 1177 with only a force of about a thousand men. The stronghold remained in the possession of the order (which was bound by vows of chastity, poverty, and obedience) until the suppression of the Knights Templars in 1313. It then passed into the hands of the Prior of Down, and is mentioned by Archdall in his “Monasticon Hibernicum” as a religious house. Upon the abolition of the monasteries the reversion of the castle and manor, with a yearly rent of £6 13s. 4d. reserved out of it, was granted to Gerald, Earl of Kildare.

In 1516, however, it appears to have been in the possession of O’Neill, who fortified it, with a boast he would hold it against the Earl of Kildare, at the same time sending to the King of France to come and help him to drive the English out.

The following year Gerald, 9th Earl of Kildare, and Lord Deputy, marched into Lecale and took Dundrum by storm, but it seems almost immediately to have reverted to the Magennises, who repaired it. In 1538 it was retaken along with seven other castles by the English, commanded by Lord Deputy Grey, who says: “I took another castell, being in M’Geeon’s countrie called Dundrome, which, I assure your lordship, as it standeth is one of the strongest holds that ever I saw in Ireland, and most commodious for defence of the whole countrey of Lecayll, both by sea and land, for the said Lecayll is invironed round about with sea, and no way to go by land into the said countrey but only bye the said Castle of Dundrome.”

After this the castle appears to have remained in the hands of the Crown for a few years. In 1551, we learn from the records of the Privy Council that Prior Magennis was seized and imprisoned in Dundrum Castle by Roger Broke without order of law. Six years later Lord Deputy Sussex asked that Lecale with the Castle of Dundrum might be granted to him in fee-farm for ever.

But again in 1565 it was occupied by the great Shane O’Neill, who placed his own ward in it for defence, and the Magennises (with whom O’Neill was intimately connected) were in possession of the stronghold in 1601, when Phelim Magennis surrendered it to Lord Mountjoy.

O’Neill is said to have been a constant visitor at the castle while it was possessed by the Magennises, Lords of Iveagh, and after a night of revelry would indulge in a strange kind of bath, by being buried to his neck in the sands on the shore of the bay.

Four years subsequently to the stronghold passing into the hands of the Crown, Lord Cromwell was commissioned to be governor and commander of Lecale and the tower and castle of Dundrum.

In 1636, Lord Cromwell’s grandson, Thomas, Lord Lecale and 1st Earl of Ardglass, sold it to Sir Francis Blundell, from whom it descended by marriage to its present owner, the Marquis of Downshire.

Sir James Montgomery fought the Irish on the shore at the foot of the castle hill 1642, and placed a garrison in the fortress to protect the district. At this time Dundrum belonged to the Blundells, who afterwards built the now ruined mansion adjoining, and the ancient stronghold was finally dismantled in 1652 by the order of Oliver Cromwell.