In a graveyard just north of St. Brigid's Cathedral in Kildare town, a small rectangular hollow in the ground marks what was once, by tradition, one of the longest-burning sacred fires in early medieval Ireland. The hollow measures roughly four and a half metres by three and a half metres, enclosed by a low rubble wall no more than half a metre high. It is, by any measure, an underwhelming remnant, and that disproportion between the physical evidence and the historical claim is precisely what makes the site worth pausing over.

The tradition holds that a perpetual flame was tended here from the time of St. Brigid, the sixth-century abbess whose monastery at Kildare, whose very name derives from the Irish "Cill Dara" meaning church of the oak, became one of the most influential religious houses in early Christian Ireland. That fire, maintained by communities of women, continued to burn until the sixteenth century, when it was apparently extinguished during the upheavals of the Reformation period. The structure that housed it, known as a fire house, does not appear on the first edition Ordnance Survey six-inch map of 1838, suggesting it had already been largely forgotten or dismantled by then. By the time of the 1939 edition, however, the site was marked, if only as "Fire house (Site of)". Old sketches recorded by Bradley and colleagues in 1986 show the gable end of a building still standing at some earlier point, but nothing of that survives today beyond the shallow hollow and its low enclosing wall.