What looks at first like a slight irregularity in the ground is in fact a rath, the Irish term for a ringfort, a type of enclosed farmstead typically built during the early medieval period, roughly between the fifth and twelfth centuries. Thousands of these survive across Ireland in varying states of preservation, but this one at Mornin retains enough of its original form to reward a careful look.

The site consists of a roughly circular raised area about 34 metres in diameter, enclosed by a bank of earth and stone approximately two metres wide and still standing between 0.45 and 0.8 metres high, despite being partially worn down over the centuries. What makes it a little more substantial than it might first appear is the internal revetment, meaning the inner face of the bank was deliberately lined with boulders and drystone masonry to hold the structure firm. This kind of construction points to a degree of care and permanence in how the enclosure was built. A shallow external fosse, a defensive ditch running around the outside of the bank, was still visible when the site was recorded in 1976, though it has since been infilled, most likely through agricultural activity over the intervening decades. A gap of about three metres in the eastern side of the bank is thought to be the original entrance, a detail consistent with many Irish ringforts, which typically faced east or south-east.