On October 3, 1691, William III of Hanover of England and King James II (William’s father-in-law) signed a peace treaty to end the Siege of Limerick and the Williamite-Jacobite War, securing religious freedom for Catholics. According to local legend, the treaty was signed on a block of limestone on the bank of the River Shannon near the Thomond Bridge. While the treaty was ultimately rejected by both English and Irish Parliaments (giving Limerick the nickname City of the Broken Treaty), the stone remains.

In 1865, the Mayor John Rickard Tinslay of Limerick commissioned a pedestal for the Treaty Stone just across the river from King John’s Castle, and it has sat there ever since. Carved into the pedestal is an image of the castle, topped with a dome and cross, to indicate that Limerick was a cathedral city.