That is, in a sense, exactly what makes it interesting. Somewhere in the improved pasture south of Carrickgollogan hill, with the Sugar Loaf Mountain visible on the southern horizon, a medieval field system once marked out the working landscape of this corner of County Dublin. Around 1950 the site was levelled and cleared, and whatever earthworks had survived to that point were erased entirely. Visit today and the ground gives nothing away.

The site's existence was pieced together from above rather than below. An aerial photograph, recorded in the Cambridge University Collection of Aerial Photography (reference CUCAP, BDP 22), reveals linear cropmarks to the south-east of where an enclosure once stood, patterns in the soil that suggest boundaries and divisions belonging to the same field system. Cropmarks form when buried features, ditches and banks that have been ploughed or cleared away, affect the growth of surface vegetation in dry conditions, leaving faint traces visible only from altitude. Archaeological test excavation carried out in 2002, prompted by an assessment for a proposed Dún Laoghaire Golf Course, brought the site back into focus at ground level. Excavators found medieval pottery in the fill of the fosses, the term for the ditches that defined enclosures and field boundaries in this period, confirming that whatever was organised here belonged to the medieval landscape of the Dublin hinterland. The findings were subsequently published by Byrne in 2004.

For a visitor, there is no marker, no preserved earthwork, and no access point set aside for the purpose. The value of knowing about Phrompstown is less about standing on the spot than about understanding how much of the medieval countryside has vanished without announcement. The aerial photograph held by Cambridge remains the clearest record of what was once there, and consulting it alongside the published excavation report gives a more textured picture of the site than the pasture itself ever could. Those with a particular interest in aerial archaeology or in the medieval settlement patterns of south County Dublin will find the documentary trail more rewarding than the field.