The bank that defines it has no visible entrance, no gap where a gate or timber threshold once stood, which gives the enclosure an oddly sealed quality, as though whatever was once inside simply remained there.

This is a rath, the most common type of Early Medieval settlement in Ireland, typically dating from roughly the fifth to the twelfth centuries. A rath consists of a circular earthen bank, sometimes accompanied by a ditch or fosse on the outside, enclosing a domestic space where a farming family would have lived, kept animals, and stored goods. The example at Rathnasliggeen measures thirty-two metres in diameter, making it a modest but complete specimen. Its bank runs to about eight metres across at the base, though that width is partly the result of slippage over time rather than original construction. The outer fosse, a shallow U-shaped ditch about three and a half metres wide and only twenty centimetres deep, is slight by any measure, suggesting this was never a heavily fortified site. The field in which it sits has been reclaimed for agriculture at some point, and the monument has suffered some disturbance as a result, yet the circuit of the bank remains essentially intact.