This fortress was one of the numerous strongholds of the O’Carrolls of Ely O’Carroll. The derivation of the name, formerly Biorra, is doubtful. Bir signifies “water,” birra = “abounding in wells,” or “fountains of water,” bir = “a spit,” bior = “the brink of a river,” and the name may have originated from any of these words.

The town is situated on the right bank of the Little Brosna River at its juncture with the Birr rivulet. It is in the barony of Ballybrit, King’s County, sixty-two and a half miles west-south-west of Dublin.

The O’Carroll’s stronghold, called the “Black Castle,” stood some sixty yards north-west of the present building on the high bank of the river. The principal tower was raised on an artificial mound, and in 1627 Sir Laurence Parsons added a watch tower, which stood on thirteen corbels, projecting on the outside, and was higher than all the other buildings. The dungeon of the stronghold was situated in the Black Castle, but this older fortress has long since been demolished.

In 1620-21 Sir Laurence Parsons made a great many additions to the castle. He erected a tower 46 feet long and 25 feet broad, at each end of which an arch of hewn stone gave entrance to the fortress. The present hall, which is reached by a flight of stone steps under a vaulted vestibule, is the centre part of this tower, as it is also that of the present mansion.

In the following two years Sir Laurence also built a porter’s lodge, known as the “Garden House,” fitted up a drawing-room and made a garden and orchard.

In 1624 he built a new line of offices, which formed one side of the courtyard, and in which was a kitchen, &c. Another side of the enclosure was occupied by the stables, which extended along the river, south of the Black Castle.

On the north was a double wall filled up with earth, and having a gateway in the centre.

Sir William Parsons threw all these buildings down in 1778.

The castle was enlarged and remodelled under the direction of Mr. J. Johnstone, architect, who altered the entrance to the back of the building, away from the town.

Sir Laurence Parsons had also added a “French Flanker” in 1627, but on what site is not known.

The Annals of Clonmacmoise record that Byrre Castle was besieged in 1207 by “Moriertagh Mac Bryen an Sleyve,” who burnt the whole town.

Ely O’Carroll was granted to FitzWalter by Henry II., nevertheless King John re-granted it to William de Braosa in 1200, and FitzWalter had to buy it back to regain possession.

It shortly afterwards passed into the hands of Hugh de Hose or Hussey.

The English rebuilt and enlarged the stronghold in 1213.

In 1432 the Earl of Ormond went to war with O’Carroll of Ely, and demolished his two chief castles, which most likely were Birr and Leap, for in spite of Royal grants the stronghold remained in the possession of the O’Carrolls.

A dispute arose about the chieftainship of the sept in 1532, the senior branch of the family holding Birr Castle.

Ferganainm O’Carroll, the son of the late chief, enlisted the aid of the Earl of Kildare, whose daughter he had married, and together they laid siege to Birr. The Earl received a bullet in his side from the garrison. It is said that a soldier, hearing him cry out in agony, remonstrated with him, remarking he himself had been wounded three times and was none the worse, to which the Earl replied he was sorry he had not received the fourth bullet in his stead. The ball was extracted the following spring, but it is said to have hastened his end.

In 1537 Lord Leonard Grey took Birr Castle, and is reported to have received submission from O’Carroll, who was created Baron of Ely in 1552.

At the time of the plantation of Ely, Birr and its castle were granted to Sir Laurence Parsons in 1620, and the same year his steward arrived to make preparations. Shortly afterwards O’Carroll appealed in vain.

In 1641 Sir William Parsons was made Governor of Ely O’Carroll and the Castle of Birr, which latter he garrisoned with his tenants.

He put the place at once in a state of defence. He raised a flanker behind the stables, and erected scaffolds inside the castle for the garrison to fight from.

After some skirmishing the fortress was closely besieged in 1642, and of the nine hundred people in town and castle many died of starvation, while others were reduced to eating dogs and cats.

At length the Earl of Ormond sent a detachment to its relief, but early the next year General Preston approached the stronghold with artillery and troops.

He reconnoitred the town from Drumbawn Hill, and after firing a few shots encamped in the neighbouring woods. On the second day of the siege he sent a messenger to the Governor to inquire if he held the castle for the King or the Parliament, and asking to be allowed to garrison it for his Majesty’s use.

Sir William replied that he had not heard of any difference from his Majesty or from the Parliament, and that he held his commission as Governor of Ely O’Carroll.

At this reply Preston entrenched, and next day began to bombard the fortress in earnest. The following night a mine was commenced under the direction of a mason who had been employed in the castle. The garrison, hearing the noise, fired on the sappers, but the darkness prevented the shot taking effect, and in the morning they were underground.

Preston continued firing, and destroyed much of the wall and one of the flankers. He said he would break down the fortress about the Governor’s ears. Some of the balls found in the masonry weighed 9 lbs. each.

Under cover of a parley the defenders of the mill were withdrawn, and the garrison held out for two days after they had been undermined. A conference was held and the besieged were granted honourable terms.

Lord Castlehaven conducted them to Athy. They numbered about eight hundred men, women, and children.

Preston seems to have retained possession of Birr until 1645, when for five years it was held by the Confederate Catholic forces.

It was taken from the Irish in 1650 by General Ireton, the enemy having burnt it before retreating. The Marquis of Clanrickarde tried to retake it in vain.

In 1688 Birr was so infested with robbers that Sir Laurence Parsons took some of his neighbours and tenants inside the castle and closed the gates. This act was magnified to the Government by his enemy, Colonel Oxburgh, who obtained an order from the Lord Lieutenant to put a garrison in the castle.

Oxburgh demanded admittance, and Sir Laurence refused until he should hear from Lord Tyrconnel. A siege then began, and when they attempted to undermine the fortress terms of capitulation were agreed upon.

Both terms of surrender (1643-1688) are preserved in the castle and have been published in the Report of the Historical MSS. Commission.

Sir Laurence and some of his tenants were imprisoned in the fortress. He was tried for high treason and several times reprieved. He was liberated after the Boyne, and appointed High Sheriff for the King’s County.

In 1690 the castle garrison, being English, was summoned, but after a parley the enemy retired.

Later the same year it was attacked by Sarsfield, who fired all day on the stronghold. The marks of the shot are still to be seen upon the castle walls. The besieged, under Captain Curry, held out until reinforcements arrived.

The English army, passing through Birr in 1691, left four hundred wounded men in the castle for two months.

Sir Laurence Parsons died in 1698.

The second Earl of Rosse succeeded to the estates in 1841. His experiments towards improving the reflecting telescope had been begun in 1827 at Birr Castle. He employed local workmen, and the tools, machinery, furnaces, ovens, &c., were all constructed on the spot, many of which are still to be seen.

At length, after many failures, two specula were cast in 1842-43. They each measured 6 feet in diameter, weighed 4 tons, and were of 54 feet focus.

The tube in which one was mounted is 58 feet long and 7 feet in diameter. It is slung on chains between two piers of masonry, and the telescope is moved and supported by a complex system of cast-iron platforms, triangles, and levers.

It is the largest telescope in the world, and cost about £20,000 to construct. Observations were commenced in February, 1845. There are several smaller telescopes at the castle as well.

The present Earl of Rosse is the third Earl, and, like his father, is an eminent scientist.