The earthwork measures approximately 36 metres from north-northwest to south-southeast and 43 metres from east-northeast to west-southwest, enclosed by what remains of a low earthen bank and shallow external ditch, or fosse. Time and agricultural activity have taken their toll on the structure; the bank has been worn down to little more than a scarp along its northwestern edge, whilst the interior ground slopes gradually from southwest to northeast.

This site presents something of a puzzle for archaeologists and historians. When the first edition Ordnance Survey maps were drawn up in the 19th century, the feature was recorded simply as part of a larger field system rather than being marked as an antiquity. It’s only through modern aerial photography, particularly a Digital Globe image from November 2011, that the rectangular outline becomes clearly visible from above, revealing what ground-level observation might easily miss.

The presence of an external fosse suggests this may have been a defended site, possibly medieval in origin. Such moated sites were often associated with Anglo-Norman settlement patterns in Ireland, serving as fortified farmsteads or minor manor houses. However, without excavation, the exact date and purpose of this Mullanakill earthwork remains uncertain, leaving it as one of many intriguing but understudied archaeological features dotting the Irish landscape.