The one at Crosserdree, on a south-facing slope of a ridge in County Westmeath, went considerably further. It is trivallate, meaning it was defended by three concentric banks with two intervening fosses, a level of elaboration that in early Irish society typically indicated a settlement of some status or wealth. The enclosed area is roughly 48 metres north to south and 42 metres east to west, substantial enough to have housed a farming household and its livestock, and the site still commands good views to the south-west across the surrounding landscape.

The three rings of earthwork survive in varying states of preservation. The inner bank is low and has been partially dug into along the northern quadrant, and the middle bank shows disturbance across the north-west to north-east arc. The outer bank fares worst; it is only clearly visible between the south and west, and from west around to north it has been reduced to little more than a scatter of boulders marking where it once stood. Despite this erosion, the original entrance arrangement is still legible on the eastern side: a gap 3.4 metres wide through the inner bank leads onto a causeway of similar width crossing the inner fosse, and a corresponding gap of 2.8 metres breaks the middle bank to complete the approach. A field fence running north-west to south-east now cuts across the eastern side of the monument, one of the more commonplace ways in which later agricultural boundaries have quietly colonised older features in the Irish countryside.