What they did not record, on any edition of their six-inch maps, was an antiquity. And yet beneath and within that ring of trees sat the remains of a rath, a type of ringfort consisting of a circular earthen enclosure that served as a farmstead during the early medieval period, typically between the fifth and twelfth centuries. The fact that it went unrecognised as such for so long is perhaps the most telling thing about it.

The site sits on grassland in the townland of Cartroncroy, with the boundary fence between Cartroncroy and the neighbouring townland of Doonis running just five metres to the west. What survives is a roughly circular area of approximately 32 metres in diameter, measured northwest to southeast, enclosed by a substantial earthen bank with a slight external fosse, the shallow ditch that would originally have reinforced the bank as a defensive or demarcating boundary. Along the northern, eastern, and southern sides, the bank has been worn down to little more than a scarp, a low eroded slope rather than a standing feature. At the southeast, there appears to be a possible outer bank and fosse, though these are considered likely later additions rather than original construction. The area around the monument has also been disturbed by quarrying, which has further complicated the picture. The most plausible explanation for the tree-plantation appearance on the 1837 map is that the site was deliberately planted up as a tree ring sometime after 1700, a practice occasionally applied to old earthworks, whether to mark field boundaries, provide shelter, or simply make use of ground that resisted ordinary cultivation. That repurposing is what preserved its outline on the historical record, even as it obscured the original nature of the structure.