At Tonmoyle in County Galway, a double-banked rath sits in level grassland at the edge of bogland, and a later field boundary cuts straight across it at the north-east and south-east, east of which the monument simply disappears from view. Whatever survives does so only to one side of that intrusion, as though the monument had been folded away.

A rath is an early medieval enclosure, typically circular or near-circular, defined by one or more earthen banks with a ditch, known as a fosse, between them. Such enclosures are associated broadly with the period from around the fifth to the twelfth centuries, and would once have enclosed a farmstead or small settlement. The Tonmoyle example is well-preserved where it does survive: a subcircular form measuring roughly 52 metres east to west and 50.5 metres north to south, with two banks and an intervening fosse still legible across its southern arc. The inner bank runs from the south-east through south to south-west, while the outer bank is visible only along a shorter stretch from the south-south-east to south-west. Elsewhere, rather than a built-up bank, the enclosure is defined by a scarp, a natural-looking slope that in fact marks the edge of the original earthwork as it has settled and eroded over the centuries.