2025 was the centenary of the report of the Irish Boundary Commission established by Article 12 of the Anglo-Irish Treaty of 1921. The Commission was an expedient attempt to resolve whether the controversial six-county border of Northern Ireland of 1920 should be amended. The Government of Ireland Act of 1920 had defined Ulster as the six most Protestant and unionist counties in north-east Ireland. However, the 1922 Irish Free State Constitution Act had made the new Irish Free State co-terminous with the whole of Ireland. Through Article 12 it gave Northern Ireland the option of contracting out of the Free State subject to the proviso that the boundary should be revised. The fact that the final report of the Boundary Commission in 1925 was secretly buried to prevent embarrassment to the new Irish Free State; to avoid causing further anger on both sides in Northern Ireland and to provide Britain with a quieter life by removing the final vestiges of its Irish question should not understate its significance. The ratification of the 1920 border in the Ireland (Confirmation of Agreement) Act in December 1925 arguably marks the high-water mark of the Irish nationalist project as well as the practical maximum level of rejection of this project by Ulster unionism.