Sacred cows, severed heads and smashed pianos

At 1.32am on March 8th, 1966, Admiral Nelson, who had stood high above O’Connell Street in Dublin for nearly 160 years, fell to earth. After the momentary silence that followed the explosion, there was an echoing thud as his falling soot-blackened body struck the base of the column, severing his head and sword. As a symbolic act, it was potent in its simplicity and pleasingly literal: if they build a statue, we can knock it down; if they make it, we can break it.

Two fragments of Nelson's Pillar, which was blown up by a dissident IRA group, feature in Art Under Attack, a new exhibition at Tate Britain, in London, about iconoclasm, or image-breaking. They form part of an exploration of the history of physical attacks on art in Britain, and on symbols of British power abroad, since the 16th century.

Perhaps unsurprisingly, Ireland has a strong presence. In Dublin particularly, iconoclasm and public statuary have been constant bedfellows. Nelson will find company at the Tate in William III, whose lead head is displayed alongside a marble plaque of military motifs – quiver, arrows, gloves – expertly evoked by the master carver Grinling Gibbons.

These both survive from the equestrian monument to the king that stood for more than two centuries on College Green. It was a focal point for political gatherings, as recorded in Francis Wheatley's colossal painting The Dublin Volunteers on College Green, 4th November, 1779, also on loan to the exhibition from the National Gallery of Ireland.

The final, fatal bombing of that statue, in 1928, was only the last in a long line of ingenious and sometimes humorous protests against the looming king: he had mud smeared on his face; a straw figure was set astride the king; his baton was stolen. Like Nelson, who weathered 1916 with only a smattering of bullet holes to the lip and withstood attack by flame gun in 1955, William was a survivor. In 1836 he temporarily lost his head when assailants made a hole in his horse and filled the cavity with a chemical explosive.

William’s lead head is joined by that of William Duke of Cumberland, the “butcher of Culloden”. This is the only reminder, other than his triumphant outstretched arm, now in Birr Library, of the statue that dominated the centre of the Co Offaly town from 1747. It was finally removed in 1915, after protests from Scottish soldiers stationed at a nearby garrison.

Irish visitors to Art Under Attack may snigger at the sight of a portrait of Oliver Cromwell hanging upside down, as it did in the collection of the strongly monarchist Prince Frederick Duleep Singh in the early 20th century. Cromwell was a dedicated iconoclast who, in a ripe piece of Puritan propaganda, was said to have scaled a ladder at Peterborough Cathedral, when others refused, to smash a hard-to-reach image of a crucifix.

These iconoclastic treasures sit among dozens of others. The lifelike late-medieval Statue of the Dead Christ – eyes half-open, tongue clearly visible, veins popping and drops of blood congealing on his side – is being shown for the first time in public. Discovered in 1954 during post-Blitz excavations, he lay under the chapel of the Mercers’ Company guildhall for 400 years, buried to protect him from further attack after his arm, feet, hands and crown of thorns were hacked off and a large X was carved on to his bony chest.

Stained glass has travelled from Christ Church, in Oxford, still in rainbow shards from having been laid on the ground in 1651 and "furiously" stamped on "with violent zeal" by Canon Henry Wilkinson. They are shown alongside censored books from the British Library, paintings slashed by suffragettes, attacked works from the Tate's collection, and the charred or twisted remnants of the radical 1966 Destruction in Art Symposium, including a piano that Raphael Montañez Ortiz destroyed for the artwork that became known as the Duncan Terrace Piano Destruction Concert.

People’s motives for attacking art varied. The complex, sometimes contradictory reasons for iconoclasm encompass religion, politics and aesthetics. Above all, the show suggests that iconoclasts believe in the power of the symbol, reinforcing its potency and affirming art as a cultural force able to shape social and political life.

The iconoclast could even be cast as a strange breed of art lover. The most beautiful objects from the dissolution of the monasteries, for example, were often remade into personal items: an elaborate chalice became a bejewelled salt cellar.

Even William Dowsing, the iconoclast general employed during the English puritanical purges of the early 17th century, was not above some furtive art appreciation. His journals, documenting his nine-month rampage around churches and chapels, suggest he understood the allure of the idols he showed such dedication to destroying. In this sense, iconoclasm is the shadow of art and bears witness to its continuing importance. Image wars are still fought, from the controversy about the Danish cartoons of Muhammad to the toppling of Saddam Hussein's statue in Baghdad.

Art under Attack: Histories of British Iconoclasm runs until January 5th

Ruth Kenny is an assistant curator at Tate Britain