The southern tower consists of three storeys corresponding with those in the keep, and had formerly doors opening from the main rooms. Next the southern wall is a curious slit in each floor just wide enough to permit of a ladder giving access to the apartment above or below. The ground floor in this tower is of very small dimensions, being about 3 feet square.
The walls of the keep slope considerably at the outside base so as to prevent an enemy getting out of gun shot by closing up to the building. Large modern windows now light each floor, and the whole is in excellent preservation.
A flue runs in the thickness of the wall on the north side, which is crowned by a handsome brick chimney, evidently added when the Elizabethan dwelling-house which adjoins the castle was erected. A still more modern house has been added to the north of this building, so that at present three distinct periods are represented by the castle and houses, which are all joined together.
The remains of an old wall near the fortress points to its having once been of larger dimensions. Tradition states that an underground passage leads from the castle to a lodge near the roadway. Some fine old yews of great age adorn the lawn, similar to those which are to be seen near Maynooth Castle.
Locally it is believed that Barberstown was once the residence of the King of Leinster, but its architecture does not bear out the tradition.
In 1622 William Sutton, of Barberstown, is mentioned in an inquisition, and in 1630 it is stated that he held it as tenant of the Earl of Kildare.
Nicholas Sutton was in possession of the castle in 1641, and at a subsequent date it must have passed to the Crown, who granted it in 1666 to John King, first Lord Kingston.
His son Robert, the second Baron, was exempted from mercy by Tyrconnell’s proclamation, and his estate sequestered in 1689.
Richard, Earl of Tyrconnell, then became possessed of the fortress, and, strange to say, that although he could only have retained it until he was attainted in 1692, yet it was known for many years as Tyrconnell Castle. Lady Tyrconnell retained some of her husband’s lands in the neighbourhood to a much later date.
Bartholomew Vanhomrigh, Esq., of Dublin, father of the famous Vanessa, bought Barberstown from the Crown in 1703 for £1,300. James Young was the tenant at the time, and the property is thus described: “In the parish of Straffan, distant from Dublin ten miles, Naas 5, and Manooth 3; is Arable Medow and Pasture, on it 1 Castle in repair, with a large stone House adjoyning, and Orchard, also 8 Cabbins, with Gardens.”