It measures roughly thirty metres north to south and twenty-seven and a half metres east to west, defined by a low enclosing bank that has survived in fair condition. A possible entrance may be traced at the south-south-west, though the evidence is tentative rather than certain.

The structure is a rath, the most common type of Early Medieval settlement monument in Ireland. A rath is essentially a circular or near-circular enclosure formed by one or more earthen banks, often with an external ditch, and was typically the farmstead of a single family of some local standing during the period roughly between the fifth and twelfth centuries. Thousands survive across the island in varying states of preservation, ranging from imposing multibanked examples to modest single-bank enclosures like this one at Ballagh. The very ordinariness of the form is part of what makes individual examples interesting; each represents a domestic life rather than a monument, a working farm that gradually became absorbed into the field systems around it. This particular rath, modest in scale and sitting quietly in the Galway grassland, would have functioned in exactly that way, its bank marking a boundary between a household's private space and the wider landscape.