The earthwork at Slane Beg appears on an 1837 Ordnance Survey map as a D-shaped enclosure, with one noticeably straight side running to the north-west. By the time surveyors revised their maps in 1913, that angular outline had been recorded as fully circular. Whether the ground changed, the cartography improved, or earlier observers simply drew what they expected to see is not entirely clear. The discrepancy is small, but it is the kind of thing that lingers.

A ringfort, or rath, is an enclosed farmstead typical of early medieval Ireland, generally dating from roughly the fifth to the twelfth century, consisting of one or more earthen banks with a surrounding ditch, called a fosse, enclosing a roughly circular area of domestic or agricultural use. The example at Slane Beg measures approximately twenty-nine metres in diameter. When described in detail in 1980, the enclosing bank was already showing considerable damage: quarrying had eaten into the eastern and south-eastern arc, leaving a depression that is still visible, and the bank had been reduced to little more than a scarp across several stretches. Only the southern and south-western portions retained any real height. The fosse, the ditch that would once have reinforced the bank on its outer edge, had by that point faded to very faint traces running from the north-north-east around to the east. Several gaps interrupt the bank at the north-west, north-north-east, and north-east, though none of them can be confidently identified as the original entrance. A modern field fence and a drain cut across the interior from south-south-east to south-south-west, and a naturally formed ridge runs north-west to south-east through the enclosed space, giving the ground inside an irregular, uneven character.

The site sits on a gentle rise in undulating pasture, with open views northward and westward toward Frewin Hill. Slane More Hill closes the view to the east and south. From aerial photography the earthwork is visible as a partially tree-lined feature abutting a field boundary to the south-south-east, the trees picking out the line of the surviving bank more clearly than the ground itself might suggest.