What makes it quietly strange is the degree to which its outline has shifted over time, not through natural erosion alone but through sustained human intervention, so that surveyors visiting just four years apart in the late twentieth century recorded what amounted to two noticeably different monuments.

Ringforts, known in Irish as raths, were typically circular or oval enclosures defined by one or more earthen banks, built during the early medieval period as farmsteads or defended homesteads. The one at Simonstown was already showing signs of alteration when the Ordnance Survey mapped it in 1837, depicting an oval earthwork with field boundaries extending to the south-west and north-west. By the revised 1913 edition, the same monument appeared penannular, meaning the enclosing bank had a gap, open to the north-west. When fieldworkers examined it in 1979, they found a small oval area roughly 26 metres east to west and 17 metres north to south, with a bank of earth and stone best preserved along its southern and western arc, and clear evidence that the bank had been quarried to the west and north-east. A lone upright stone near the western scarp was interpreted at the time as a cattle scratching post. When a second team returned in 1983, what they described was a larger, roughly D-shaped enclosure, approximately 35.5 metres north-east to south-west and 27 metres north-west to south-east, its interior disturbed by extensive digging and its straight north-eastern edge suggesting deliberate modification rather than gradual wear. The discrepancy between the two accounts may partly reflect different methods of measurement, but it also points to a monument that was being actively quarried and reshaped even within the period of modern record.

A second ringfort lies approximately 210 metres to the north-north-east, suggesting this ridge was considered significant ground over a long period. The Simonstown rath is still visible from aerial photography as a D-shaped earthwork, the remaining curvilinear scarp tracing its older, rounder outline some distance beyond the modified straight edge, like a ghost of the original form showing through the surface of the field.