On the morning of 20 May 2000, perhaps a dozen men and women holding printed placards walked into St Mary’s churchyard in the Irish town of Drogheda. They had come to protest an exhibition taking place at the deconsecrated church, which featured a provocative historical relic: the death mask of the English soldier-statesman, Oliver Cromwell.

In Ireland, the name Oliver Cromwell is remembered with unanimous horror. Under Cromwellian rule, the Irish population shrunk by a third, decimated by famine, plague and colonial policy. At the end of the Civil War, Cromwell had personally led a brutal Irish campaign designed to subdue the restive Catholic population. At Drogheda, his army massacred the entire defending garrison, burning Catholic priests alive inside a church and butchering huge numbers of civilians.

In 2000, the old tormentor was back. CROMWELL DRANK DROGHEDA BLOOD, read one placard. SATAN AND CROMWELL: LADS TOGETHER, said another. One protestor began smearing the churchyard walls with symbolic ketchup. Leading the protests was Drogheda’s deputy mayor, Frank Godfrey, sporting a broad-brimmed black hat and antique sword. He was seeking to parley with the man that everyone knew was responsible: local historian, Tom Reilly.

A year before the exhibition, Reilly attracted national attention by publishing a book which argued that Cromwell’s forces did not, in fact, massacre civilians at Drogheda or at Wexford, where another massacre is attested. Reilly argued that Cromwell’s campaign, while brutal, had not even breached the laws of war as they were understood in the seventeenth century. The book was called Cromwell: An Honourable Enemy.

In the same year, Reilly had sunk a large amount of his own money into setting up a local heritage centre in St Mary’s, a recently deconsecrated Protestant church. As a member of the Friends of Oliver Cromwell society – its only ever Irish member – he was able to secure the loan of the death mask that provoked such outrage.

‘It is a bit like bringing the death mask of Hitler to a town where he killed the Jewish population,’ the deputy mayor had told the local press who covered the protest.

Yet Tom Reilly was undeterred.

In 2002, he provoked an eerie simulacrum of the first debacle by exhibiting Cromwell’s sword in the same centre. Godfrey put on his black hat and was soon being quoted in local newspapers compared it to exhibiting Hitler’s pistol in Jerusalem. This time, he challenged Reilly to a duel with whatever weapon he chose.