It sits in level pasture, its boundaries marked not by a prominent earthen wall but by a wide, shallow fosse, the kind of ditch that once defined the outer edge of an enclosed farmstead. Without knowing what to look for, a person could walk its perimeter and not immediately grasp the scale of what they were crossing.

A rath is an early medieval ringfort, typically dating from roughly the sixth to the tenth century, built as a defended farmstead for a single family or small community. The Summerhill example is notably large, measuring approximately 94 metres north to south and 89 metres east to west, and its outline is irregular rather than the neat circle more commonly associated with the form. On the southern side, a gap around 7.2 metres wide may mark the original entrance. Whether this was a formal gateway or simply a break in the boundary is difficult to say, but the positioning on the south, which was the most common orientation for ringfort entrances in Ireland, fits a familiar pattern. The surrounding landscape of Ballinrobe and the districts bordering Lough Mask and Lough Carra is well documented as an area of considerable early settlement, and a site of this size would have represented a substantial household within that world.