In 2010, a San Francisco art dealer advertised what he thought was an American battle scene for sale on eBay. Art historian Niamh O’Sullivan instantly recognised it as the painting she had been trying to track down for seven years. It was John Mulvany’s The Battle of Aughrim, lost to the public since it had last been exhibited in Denver in 1914.

James Gorry of Dublin’s Gorry Gallery, which specialises in repatriating Irish art from abroad, bought the painting and subsequently sold it to a private collector in Ireland.

How a canvas measuring 35”×78” could disappear for a century remains a mystery but then Aughrim’s significance in Irish history is often overlooked – eclipsed by the more famous but less-decisive Battle of the Boyne. After William III’s victory at the Boyne in 1690, the largely Catholic Jacobite army retreated to Limerick – the strategic key to the west of Ireland. General de Ginkell, commanding the Williamite forces, captured Athlone in June 1691 and proceeded to advance towards the Jacobite base at Limerick.

John Mulvany.

He found his way blocked by 20,000 men commanded by French General Saint-Ruhe; the last time an Irish army would take the field with artillery and cavalry deployed and banners bravely flying.

It was the bloodiest battle ever recorded on Irish soil

Though the Jacobite army fought with tenacity and courage, the day’s end would see Saint-Ruhe dead, many of his senior officers captured or killed, and the dream of Catholic governance in Ireland destroyed.

It was the bloodiest battle ever recorded on Irish soil, with a death toll of over 6,000 men. In the Irish language, Aughrim is remembered as “Eachdhruim an áir” (Aughrim of the slaughter).

Two hundred years later, in the 1880s, the struggle for Irish independence was still ongoing, with the Land League agitating for land reform and London subjected to a dynamiting campaign (funded by the American-based Clan na Gael).

Against this background, celebrated Irish-American artist John Mulvany returned to the land of his birth to research his giant canvas of the battle. Mulvany was born in Diralagh, Co Meath, in 1839. A child of tenant farmers, he emigrated to New York in 1851. He was old enough for the ravages of the famine to have made a searing impression on him.

He was allowed access to the Tower only grudgingly – his strong republican views were no secret

He grew up with strong nationalistic leanings and was a lifelong member of Clan na Gael. During the American Civil War, he was employed as a sketch artist for a Chicago newspaper and he rose to real fame with his 1881 battle scene Custer’s Last Rally. This led to Mulvany securing a commission from the Irish Club of Chicago to paint the Battle of Aughrim. As well as walking the battlefield itself, Mulvany travelled to England to research the uniforms and weaponry of the period at the Tower of London.

He was allowed access to the Tower only grudgingly – his strong republican views were no secret.

The completed work owes more to Mulvany’s desire for clear narrative than to his historical research. There is no record of green-coated Irish troops fighting at Aughrim, and the Williamite cavalry would have been more variously uniformed than they appear in the painting. For all that, it is a painting that brings 17th century warfare rousingly to life – full of swirling smoke, clashing steel and thundering hooves.

Perhaps more to the point, it met with universal acclaim from Irish nationalists upon its completion in 1885. Michael Davitt wrote to Mulvany, declaring: “You deserve the thanks of the entire Irish race... your genius has transferred to canvas the dauntless bravery of those ‘Who died, their land to save, on Aughrim’s slope’.”