Ringforts, known in Irish as raths, were enclosed farmsteads built predominantly during the early medieval period, typically defined by one or more earthen banks enclosing a roughly circular interior. The Loughagar Beg example sits on a low rise near the summit of a high ridge, a position that would have afforded its original occupants clear views to the north and east, which was likely the point.

The monument had a reasonably well-documented decline. The first Ordnance Survey six-inch map of 1837 recorded it as an oval-shaped earthwork, annotated simply as "fort". By the revised twenty-five-inch edition of 1913, it still appeared as a broad oval with approximate dimensions of 42 metres east to west and 41 metres north to south, enclosed by a bank. A field report compiled for the Office of Public Works in 1965 described a roughly circular rath with an uneven interior, which suggests the bank was eroding but still legible in the landscape. That same year, H. A. Wheeler drew a sketch profile of the monument, a record that now carries more weight given what followed. By 1970, surveyors reported no surface remains visible at all. Within the span of a single lifetime, the earthwork had been levelled entirely.

What makes the site quietly interesting today is that erasure from the ground surface is not quite the same as erasure from the record. Aerial photography has since revealed the monument as a partial cropmark, an arc of differential plant growth running from the north-west to the east, tracing the ghost of the original perimeter. Cropmarks of this kind appear when buried features, such as the compressed soil of an old bank or ditch, affect how crops grow above them, producing variations in colour and height that are invisible at ground level but legible from the air. The rath at Loughagar Beg is now most coherently understood as an aerial phenomenon rather than a physical one.