About half a mile to the south-east, on the south bank of the river, a Romanesque church sits quietly at the centre of an oval graveyard, enclosed not by a wall in the conventional sense but by an earthen bank some three metres wide and one and a half metres high, its outer face revetted with drystone walling. That D-shaped enclosure, measuring roughly 18 metres north to south and 41 metres east to west, is itself a significant feature; early Irish ecclesiastical sites frequently used curvilinear enclosures of this kind to demarcate sacred ground, and the earthwork here preserves that older logic in unusually legible form.

The church is considered one of the latest Romanesque structures at Glendalough, which already sets it apart from the site's earlier buildings. Its founding is attributed to St Lorcán Ua Tuathail, better known in the Anglicised form as St Lawrence O'Toole, who is said to have established it for Augustinian Canons in 1162. The Augustinians at this period were adopting the Arroasian reform, a stricter observance originating from the monastery of Arrouaise in northern France, and this community followed suit probably shortly after 1163. O'Toole was Archbishop of Dublin from 1162 until his death in 1180, and his connection to Glendalough ran deep; he had been a monk there before his elevation to the archbishopric. The nave and chancel plan of the church, a simple two-cell arrangement common in Irish Romanesque architecture, reflects the modest scale typical of houses affiliated with this reform movement.