What began as routine monitoring by Celie O’Rahilly of Limerick Corporation quickly evolved into a full-scale excavation lasting until September 1991. The team, led by archaeologist Wiggins, was initially tasked with finding the remains of the castle’s eastern curtain wall and bastion, both demolished around 1800. The excavation area stretched approximately 47.5 metres from north to south, running from the castle’s north-eastern tower to the bastion’s southern wall, with widths varying between 17 and 30.5 metres.

What emerged from beneath centuries of development was far more significant than the expected castle foundations. The excavations revealed part of a large ringwork enclosure dating to around 1175–6, predating King John’s Castle by several decades. This earlier fortification, built by the Anglo-Norman garrison, featured a stone-revetted bank and a broad external ditch running east to west, positioned at right angles to where the castle’s eastern curtain wall would later stand. These twelfth-century defences represent some of the earliest Anglo-Norman military architecture in Limerick, constructed during the initial phases of the Norman conquest of Ireland.

The ringwork’s remarkable preservation allowed archaeologists to trace both the defensive bank behind its retaining wall and the ditch that ran in front of it, though both features showed signs of disturbance from countermines dug during the 1642 siege of the castle. This discovery fundamentally changed our understanding of the site’s history, revealing that the location had been strategically important for nearly a century before King John ordered the construction of his imposing stone castle in the early thirteenth century.