What had long been recorded as a ringfort turned out, on excavation, to be a medieval enclosure built directly on top of something far older, and the layers of activity compressed into that roughly 50-metre square of ground span at least three distinct periods, each one cutting into, reusing, or simply ignoring what came before it.

The site came to light in August 2005 during testing associated with the N6 Kilbeggan to Athlone dual carriageway, and excavations led by Tim Coughlan of Irish Archaeological Consultancy Ltd. ran from October 2005 through to April 2006. At the centre of everything was a probable Bronze Age ring-barrow, a type of funerary monument typically consisting of a low mound or flat platform enclosed by a circular ditch, used for burial during the Bronze Age. At Cappydonnell Big, this took the form of a circular enclosure roughly 14 metres in diameter, with an outer ditch about 2 metres wide and a smaller inner ditch of around 7 metres diameter. A stone-lined cist, a small box-like grave formed from upright slabs, sat to its north and appeared to contain a disturbed cremation. Part of a human skull was also recovered from the lower fills of the barrow, though whether it belonged to the original burial or was displaced by later activity is unclear. In the medieval period, the barrow ditch was partially recut to accommodate an industrial furnace, and the charcoal-rich material recovered from that area included burnt human and animal bone, nineteen amber beads, and traces of metal and slag. What exactly was being produced there remains uncertain pending further environmental analysis. The subrectangular enclosure surrounding all of this does not comfortably fit the profile of a ringfort, a platform ringfort, or a moated site, despite sharing features with each. Post-medieval plough furrows and a corn-drying kiln, the latter apparently repurposed at some point as a soak pit and filled with large stones, add further texture to an already complicated stratigraphy. Near the surface, badly disturbed human remains with no visible grave-cut suggest an informal burial of uncertain date, possibly much later than anything else on the site.

The excavators themselves described the results as something of an enigma. Very few artefacts were recovered from the main enclosure ditch, which was largely sterile, and the site's final interpretation was expected to depend heavily on environmental sampling and radiocarbon dating rather than finds. It is one of those places where the ground gave up enough to raise serious questions and not quite enough to answer them.