This is where, on 8th September 1798, somewhere in the region of a thousand Irishmen are believed to have died, most of them not in battle but in what followed it, a systematic killing that began the moment organised resistance collapsed. The hill is not widely marked or celebrated, yet the Ordnance Survey thought it significant enough to record the locations of 'Soldiers Graves' on their early twentieth-century maps, quiet cartographic acknowledgements of what happened here.

The battle of Ballinamuck was the effective end of the 1798 rebellion in Connacht. A French expeditionary force of around 800 men under General Humbert, which had landed in Mayo weeks earlier and achieved a startling early victory at Castlebar, had marched east in the hope of linking up with other rebel forces. By the time they reached Longford, they were facing odds that made any military outcome impossible. General Lake commanded approximately 14,000 British troops, with a further 15,000 under Lord Cornwallis, the newly appointed lord lieutenant of Ireland, moving to cut off any retreat. Humbert drew up his combined French and Irish force of roughly 2,300 men on Shanmullagh Hill. The engagement itself was brief. The French, as prisoners of war under the conventions of the time, surrendered and were treated accordingly; 96 officers and 748 men were taken, transported by canal to Dublin, and eventually repatriated to France. The approximately 1,500 Irish fighters beside them had no such protection. Estimates vary, but around 500 are thought to have died on the hill itself, with perhaps the same number killed in the days of pursuit and reprisal that followed. The British campaign then continued westward, ending with the fall of Killala, County Mayo, on 23rd September, accompanied by further slaughter.

The asymmetry of what happened here, French soldiers spared, Irish rebels massacred on the same ground, lodged itself deeply in local memory. Ballinamuck passed into folklore across the midlands and west of Ireland, and the site on Shanmullagh Hill has continued to carry that weight, less a formal monument than a place where the ground itself is the record.