What lies beneath those trees is a rath, or ringfort, a type of enclosed settlement built throughout Ireland during the early medieval period, typically between the fifth and twelfth centuries. A bank of earth and an outer ditch, known as a fosse, defined the homestead of a farming family and offered a degree of protection for people and livestock alike. This one sits on ground that commands good views in all directions, a feature that was almost certainly deliberate.

The earthwork measures roughly 37 metres in diameter and was recorded in detail in 1970. Its bank is best preserved along the northern, eastern, and southern arcs, while the western and northern sections show signs of later interference; a modern bank was added at the upper exterior edge at some point, steepening what was already there. The fosse, too, may have been recut in relatively modern times, a reminder that agricultural landscapes are rarely left undisturbed. The original entrance survives at the south-east, where a slight causeway crosses the ditch, the gap measuring just over five metres at the top and narrowing to two metres at the base. Inside, the ground rises gently from the perimeter toward the centre, and faint traces of cultivation ridges run roughly north-north-east to south-south-west, suggesting the interior was put to agricultural use at some stage after the ringfort fell out of use as a settlement. The monument appears on the Ordnance Survey six-inch map of 1837 as an oval earthwork, and again on the revised twenty-five-inch edition of 1913, with only slight modification to its outline. Another ringfort lies approximately 75 metres to the north, making this part of Brittas an area of some early medieval density. A modern fence now crosses the perimeter at three points, and a second gap has been cut at the north, but the essential form of the place endures.