Most people walking the land would likely take it for a natural undulation. It is, in fact, the surviving remains of a ringfort, the kind of enclosed settlement that once dotted the Irish countryside in enormous numbers during the early medieval period, typically serving as a farmstead for a family of some local standing. What makes Rathsallagh quietly interesting is precisely how much has been absorbed back into the working landscape around it.

The Ordnance Survey's six-inch map of 1837 recorded the site clearly, marking it as a large circular enclosure and labelling it simply "Fort", which was the standard shorthand used by those early surveyors for monuments of this type. At that point the earthwork was apparently more legible than it is today. A low scarp, no more than 0.3 metres high, still traces the circuit of the enclosure, but along a significant arc running from the south-southwest, around through west, and out to the west-northwest, that scarp has been pressed into service as a field boundary, folded into the agricultural fabric so thoroughly that the original line of the monument is hard to separate from later land management. The entrance, wherever it once stood, can no longer be made out on the ground. A report from 1976 noted the presence of an external fosse, the shallow ditch that would have ringed the outside of the enclosure, providing both a modest defensive element and a source of the material heaped up to form the interior platform. That fosse has since been infilled entirely, leaving the site even more reduced than it was a few decades ago.