‘This lofty and massive building, which rears its high head in solemn grandeur, and seems to look down with fostering protection and watchful guardianship on the town beneath it, was built by Hugh de Lacy, about the year 1140, in the reign of John. Though some difference of opinion exists on this point – some referring it as the work of Eva, daughter of Dermot McMurrough, and others attributing it to Isabel, daughter of Strongbow, and others, to King John, &; but concurrent, circumstantial and historical evidence, fix on de Lacy as the founder. The walls of the tower are of the amazing thickness of seven feet, two inches; the inner diameter of the same ten feet, and the exterior circumference is seventy seven feet. The whole building was amply provided with loop-holes, and with arched and mullioned windows, &, from which to pour, if necessary, on their assailants the sweeping shot of artillery and musketry, or the less destructive missile.’
From the Dublin Penny Journal, Volume III, July 26th 1834

‘The only ancient relic in Carlow is “the Castle.” It is situated on a gentle eminence, overlooking the river; and is said to have been erected by Hugh De Lacy, who was appointed lord-deputy of Ireland in the year 1179. It was built after the Anglo-Norman style of architecture; a square area, surrounded by thick walls, fortified and strengthened at each corner by a large round tower. Until the year 1814, it had bravely withstood the attacks of time and war; but its ruin was effected by the carelessness of a medical doctor, into whose hands it came, and who designed to put it “in order” for the “accommodation” of insane patients. In the progress of his work he applied gunpowder, with some unexplained object, to the foundations, and in a moment completed its destruction, leaving but two of its towers, and the wall between them. Their present height is sixty-five feet, and the length from one tower to the other is one hundred and five feet; as the ruin is but one side of a square, it affords a correct idea of the large space the castle formerly occupied.’
From Ireland: its scenery, character etc. by Mr and Mrs Hall, 1840.