The ruined cathedral consists of an aisleless nave and chancel, to which a sacristy was added on the S. The nave was originally a single cell, rectangular church, with antae, belonging to the pre-Romanesque era. Its internal dimensions are approximately 14.7 m by 9.0 m, making it one of the largest such buildings in the country (along with Clonfert and Clonmacnoise). There is an early lintelled doorway in the W wall. The chancel, which has internal dimensions of 6.63 m by 11.45 m, was added about 1200, when an additional doorway was inserted in the N wall of the nave. The chancel is built of rubble masonry, but there are well-dressed quoins on the E angles, which are given a tiny chamfer.
Soon after the Anglo-Norman invasion, attempts were made to unite the diocese of Glendalough with that of Dublin. The Anglo-Normans mounted a propaganda campaign against the old monastery, since it lay in an area, which the new regime found hard to control. In a document of 1215 it was described as a 'nest of thieves and robbers'. The remodelling of the cathedral took place while the independence of the see of Glendalough was under question, and it is tempting to see the alterations as a belated attempt to raise the status and appearance of the cathedral church. The union of the dioceses finally received Papal approval in 1216, after which Glendalough was reduced to the status of an archdeaconry. The cathedral appears to have become an Augustinian house and in the 1302-6 it was described as the 'Priory of the great church of Gleydelagh', presumably to distinguish it from St Saviour's. Before passing into the care of the Office of Public Works, the cathedral fabric was in a far more ruined condition than it is today. Both the chancel arch and the E window were substantially rebuilt between 1875 and 1879.
There is a drawing in the Royal Irish Academy (3C. 30) by the 18thc topographical artist, Gabriel Beranger, which purports to show the capitals of the rear arch of the E window. One side shows various floral designs and two standing affronted animals; the other shows what appear to be a lion attacking a snake, followed by a human figure grasping foliate tendrils. The drawing was later copied by Petrie.
There is a chamfered plinth, a section of which is cut out on both sides, corresponding with a socket in the pavement, measuring 0.17 m by 0.13 m. This may have been designed either to receive the vertical supports of a rood loft or to receive the base of a detached shaft. Above a simple chamfered base are plain masonry jambs, with chamfered angles terminating in stop chamfers about 0.48 m above the base. Underneath the first arch order on each side, there is a corbel, but only the northern example is original. This takes the form of a concave scalloped capital. A chamfered impost sits above, extending across first and second orders
Nine voussoirs survive on each side of the arch. There is a filleted roll on the outer angles, with a further small, plain roll each face. The soffit has a flat section, flanked by small rolls. The E face of the order on the N side retains a number of masons' marks.
G. L. Barrow, Glendalough and Saint Kevin, Dundalk, 1972, 31–3.
Glendalough, Co. Wicklow, Official Historical and Descriptive Guide, Dublin, n.d., 26–30.
A. Gwynn and R. N. Hadcock, Medieval Religious Houses:Ireland, London, 1970, 80–1, 176–7.