St Nessan's Church: a monastic settlement is recorded as having been established on Irelands Eye in the 8th century, However, stone was not used to build churches in Ireland until the 10th century.

From - The Neighbourhood of Dublin, Ch. XXXII, 337-338) - Weston St. John Joyce

"The ruin of St. Nessan's Church on Ireland's Eye may be fitly described as an antiquarian forgery. It was an interesting ruin in 1843, when it was sketched by the late Mr. Wakeman, but soon afterwards, it was restored without any regard to its former condition or appearance, and, as a result, it is now almost impossible to identify it with the sketches of Petrie and Wakeman. It cannot even be said that the materials of the modern ruin are those of the old church, as portions which had long previously disappeared were reproduced in the restored edition. It is stated by Petrie that the doorway of the original structure was taken down in order to utilise the stones in building the Catholic Church at Howth.

St. Nessan's Church, owing to its exposed position, was in early times constantly pillaged by Danish and English marauders, and it is recorded that Irghalach, King of Bregia, was slain in one of these attacks. It is not, therefore, Surprising that, as the original ecclesiastic establishment of Howth, it was for security transferred to the mainland in 1235, from which date the church on Ireland's Eye was probably allowed to fall into decay."