The former name for this stronghold was Castle Mahon. It is situated on the River Bandon not far from the town. The present castle is said to occupy the site of the former royal rath of the O’Mahonys, Kings of Munster. It was called Rathleann, and the great Saint Fin Barr was born there. This was much anterior to the English invasion, although an inquisition held in 1584 states that the O’Mahonys came from Carbery in 1460, and seized the Crown lands, which had been forfeited by the Barry Oges in 1399.

They were, however, only returning to the country over which they had formerly ruled. The fortress is supposed to have been built by an O’Mahony.

Francis Bernard, who succeeded to the estate in 1660, threw down the ancient bawn walls, and enlarged the windows. His son, Judge Bernard, rebuilt the castle after it came into his possession in 1690.

A new brick front was added on the river side, the bricks having been made in the neighbourhood.

He was succeeded by his son Francis (usually known as Squire Bernard) in 1731, who added an eastern front to the fortress, and planted the great beech avenue. Smith, who collected his information in 1749, describes the castle as having two regular fronts of brick, with Corinthian pilasters and coignes and beltings of Portland stone.

In 1788 Francis Bernard, afterwards the 1st Earl of Bandon, pulled down the two fronts which had been added by his predecessors, and connected the old castle by a corridor (some 90 feet in length) with a mansion he erected a little to the east of the stronghold. This new part has large rooms, the library being a very handsome oval apartment.

This forms the present beautiful country seat of the Earl of Bandon. It is situated in a park about four miles in circumference, through which the Bandon River flows.

The O’Mahonys were not a powerful sept: their regular field force only numbered twenty-six horse, no gallow-glasses, and a hundred and twenty kern.

In 1575 the O’Mahony paid his respects to Sir Henry Sidney during his visit to Cork, of whom Sir Henry writes that he was “a man of small force although a proper countrie.”

Conoher O’Mahony, of Castle Mahon, threw in his lot with the Earl of Desmond during his rebellion, in which rising he was killed at the age of twenty-three.

In 1587, an inquisition held at Cork found that Conohor O’Mahownye, late of Castle Mahown, entered into rebellion with Gerald, late Earl of Desmond, and was slain therein and that he was seized of Castle Mahown and of the barony or cantred of Kineallineaky.

The following year the castle and lands were conferred by patent on Phane Beecher, son of Alderman Henry Beecher, of London.

Mr. William Weever, in his “discourse” on the Munster rebellion of 1598, records that Mr. Beecher deserted Castle Mahon during the rising.

In 1611 it seems the grant to Phane Beecher was confirmed.

The first Bernard to settle in Ireland during Elizabeth’s reign had a son Francis, who was lord of the manor of Castle Mahon, where he lived before the rebellion in 1641. He had one son, Francis, who was in possession of the castle in 1690 when Bandon was surprised and taken by Colonel M’Carthy’s men. After the town had fallen into their hands they proceeded to Castle Mahon and demanded the fortress and its stores to be given up to King James, and the garrison to surrender as prisoners.

Mr. Bernard had served many years with the Bandon Militia, and had been rewarded with a grant of land from Cromwell for military service, so that he was not likely to surrender without a struggle when the trumpeter appeared on the esplanade in front of the castle.

He had gathered his retainers and the neighbouring farmers into the stronghold, and flew the red flag from King John’s Tower.

Having received a negative to their demand, the besiegers attempted to batter in the great gate, but a discharge of musketry killing some of their number they desisted. They shook the windows and doors to try and effect an entrance.

A line of sentries were posted in front of the castle with orders to shoot any one who appeared at the windows, but the deadly fire of the besieged killed them nearly all.

Seeing that their numbers were rapidly thinning they sought cover from the out-houses in the rear, and from there they carried on an ineffectual fusilade for some time.

Finding, however, this was of no avail they retreated to the river, crossing by the ford. A pike blade and some swords of this date were recently found in a pond which lay in their route.

The brave garrison had many killed and wounded, Mr. Bernard being among those who lost their lives.

The dead Irish were collected and covered with straw in a stable until the next day, when they were buried in a disused graveyard at Killountain.

Judge Bernard succeeded his father, having been born in the castle in 1663. He changed the name from Castle Mahon to Castle Barnard.

His son, “Squire Bernard,” did much for the neighbourhood until a dispute with the townspeople about trees caused him to go and live in England.

In 1760 a sad accident took place which led to the death of little Robert Bernard, one of the sons of the house. He had climbed to the top of King John’s Tower, and as the bats and swallows flew in and out he tried to strike them with his battledore, but overbalancing, he stepped back to recover himself and fell through the trapdoor which gives egress to the summit. He died of the injuries received.

Francis Bernard was created Earl of Bandon in 1800, and Castle Barnard is still the principal residence of the Earls of Bandon.