‘The monastery of Rahan…was founded by St Carthach or St Mochuda about the year 580. A king of Cornwall, named Constantine, abandoned his throne in 588, and became a monk there, whence it would seem the name Constantine became a favourite one with the family of Molloy, who were princes of Fercall, the district around Rahan. Under St Carthach, Rahan marvellously prospered, so that 867 monks were said to have been gathered under his rule at one time, and his followers formed one of the four great orders into which the Irish monasteries were divided…The monastery of Durrow, however, became jealous of the success of Rahan, and so in 636 roused King Blaethmac to expel Carthach, who took refuge in Lismore, where he founded the see but died the next year.’
From The Journal of the Royal Society of Antiquaries of Ireland Part III, Third Quarter, 1896.

‘The ancient Irish church at Rahan – repaired for Protestant worship – has a remarkable round window, measuring about seven feet six inches in the external diameter of the circle, and it is placed about twenty-two feet from the level of the ground. It formerly lighted a chamber placed between the chancel and the stone roof. It has a circle of bead ornaments and chevron carving within the outer band-line. The ornamental sculpture is in low relief are inciso or hollow. The stone and masonry of this church are of a very superior character.’
From Lives of the Irish Saints Vol.X, by the Rev. John O’Hanlon, (Dublin, 1905)

‘The Abbey of Rahin [is] partly restored as a parish ch. It was founded in the 6th century by St Carthach or Mochuda, afterwards Bp. of Lismore, and is remarkable for its archaeological details. The visitor should notice the chancel archway, which consists of 3 rectangular piers on each side, rounded at their angles into semi-columns, and adorned with capitals elaborately sculptured with human heads. The original E. window is gone, but lighting a chamber between the chancel and the roof is a remarkably beautiful round window with ornaments in low relief. The antiquary should compare the decorations of the capitals with those at Timahoe. There are also ruins of 2 other chs., one of them containing a doorway with inclined jambs (indicative of early Irish architecture) and an arch adorned with the characteristic moulding so like Norman.’
From A Handbook for Travellers in Ireland by John Murray (London, 1866)