A rough limestone block on a stone pedestal on the western (Thomond Bridge) side of the Shannon, the Treaty Stone marks — by tradition rather than documented fact — the place where the 1691 Treaty of Limerick was signed at the end of the Williamite war in Ireland. The treaty promised toleration to Catholics on terms that the Westminster parliament subsequently abrogated, and "the broken treaty" became one of the foundational grievances of Irish nationalism in the centuries that followed.
The stone itself is irregular and unremarkable; the view across the river to King John's Castle is the better reason to walk the few hundred metres over Thomond Bridge to find it. The footpath upstream from here gives the cleanest profile of the castle's five towers against the western sky.