Most of it has been grazed flat over the centuries, reduced to a faint scarp barely above the surrounding pasture. Only in the south and south-east quadrant does the original bank still read clearly in the landscape, rising to an external height of around 1.3 metres, wide enough to suggest that this was once a deliberately engineered boundary rather than a fold in the ground.

This is a rath, the type of ringfort most commonly associated with early medieval Ireland, roughly the fifth to twelfth centuries. A rath typically consisted of a raised earthen bank and an external fosse, or ditch, enclosing a roughly circular area used as a farmstead or the residence of a local landowner. The one at Lisnagaul follows that pattern: a grass-covered bank and a fosse that still survives to a depth of up to 0.7 metres in places, though both have been considerably worn down. A north-to-south field boundary running across the western side of the monument has either cut into or absorbed part of the bank there, which is a common fate for earthworks that have been farmed around for a thousand years or more. The diameter, just over thirty-one metres north to south and thirty-two metres east to west to the field boundary, puts it comfortably within the normal size range for a single-banked rath of this kind.