Beneath and around it lie the physical traces of an early Christian monastic enclosure, the kind of site that centuries of construction, burial, and everyday parish life have a way of obscuring almost entirely. The churchyard holds a plain granite cross and, perhaps more unexpectedly, a millstone from a horizontal watermill, the type of small, water-driven mill common to early Irish monastic settlements, where a low-set wheel was driven directly by the flow of a stream rather than by a tall vertical wheel of the kind most people picture.

The site is associated with St. Brendan of Clonfert, the sixth-century monk celebrated in medieval tradition for an extraordinary ocean voyage, and his connection here was documented by Appleyard as far back as 1985. The physical evidence for an early enclosure was confirmed more concretely in 1990, when excavations directed by Swan uncovered a section of an outer fosse and inner bank, the characteristic boundary earthworks that defined the sacred and functional space of an early Irish monastery, as well as a portion of an earlier wall. Among the finds recovered were a bronze penannular brooch, a type of ring-shaped fastening common throughout early medieval Ireland and Britain, a small lead ingot, and a piece of worked antler. These are modest objects individually, but together they point to a community engaged in craft activity and everyday life on this patch of north County Dublin sometime in the early medieval period.

The Church of St. John the Evangelist stands in Tonlegee, in the Coolock barony, on the northside of Dublin city. The churchyard is the place to focus attention, where the granite cross and the millstone can be found among the more familiar furnishings of a parish graveyard. The earthwork evidence uncovered in 1990 is no longer visible at the surface, but knowing it exists beneath the ground changes the way the site reads. It is worth taking time with the stonework and the broader layout of the churchyard boundary, which may itself preserve something of the curve of the original enclosure.