Glinting in the winter sunlight, unblemished as yet by pigeon droppings, the latest work of art to occupy the Fourth Plinth in the north-west corner of Trafalgar Square was unveiled today — and in one sense it is the most old-fashioned yet. Conceived by the Nordic artists Michael Elmgreen and Ingar Dragset, Powerless Structures, Fig 101, the eighth contemporary artwork commissioned for the plinth since 1999, is a monumental bronze equestrian statue more than 4m high. Executed in a realistic figurative style, it belongs to a tradition that stretches back to the ancient world, when Rome was awash with colossal gilt-bronze portraits of emperors mounted on horseback. Yet unlike the permanent equestrian statues nearby (Francis Chantrey’s bronze of George IV; Hubert Le Sueur’s over-inflated Charles I at the top of Whitehall), Powerless Structures isn’t a portrait of a monarch, or even a greybeard general or statesman, but a young boy riding a rocking horse. When the north-west plinth was built to support a portrait of William IV on horseback in 1841, nobody could have foreseen that one day it would bear an equestrian statue like this. Raising his right arm in a gesture that alludes to the pose of the big daddy of the genre (the colossal portrait of Marcus Aurelius in the Capitoline Museums in Rome), this curly-haired kid is rapt in fantasy — play-acting at conquering the known world like a pint-sized Alexander the Great, or riding from some two-horse frontier town into the Wild West. He leans backwards as his steed rears up, imbuing the composition with sprightliness — something missing in the statue by Le Sueur, whose horse decorously raises a foreleg in a display of dressage-like control. Lost in play, Elmgreen & Dragset’s gilded youth radiates innocence — and yet the tone of the sculpture is adult and arch. The artists, who once installed a Prada boutique in the middle of the Texan desert, are gently mocking the tradition of equestrian statuary — obviously so. Nude aside from a pair of skimpy shorts held up by braces (lederhosen? hot-pants?), their boy has a camp insouciance that only enhances the work’s cheeky message. If art is an index of the times, what does this sculpture say about us? For one thing, that the age of empire, when equestrian statues could be cast with a straight face, is definitively over. It makes sport of our tendency to hero-worship warmongers by erecting statues in their honour. It also points ironically to an obsession with youth that permeates our culture: during the days of the Republic, the Romans produced portraits of grizzled strongmen with experience etched into their miens, but we choose to look at a smooth-cheeked boy dreaming impotently of world domination. Powerless Structures, Fig 101 is a scrotum-shrivelling riposte to the concept of machismo, a satire on Britain’s standing in the pecking order of the world. In places, the statue itself may look a little smooth (the uninteresting planes of the rocking horse resemble spray-painted MDF). Moreover, as a work of art, it isn’t particularly complex or poetic. But that, I feel, is its primary asset. Public art should be loud and clear. Unlike some of the previous commissions for the plinth, such as Thomas Schütte’s abstract Model for a Hotel from 2007, Powerless Structures, Fig 101 is a strong and simple idea that people will “get” in an instant, almost as quickly as it will make them smile. And for a sculpture occupying one of the most prominent public spaces in the realm, there’s nothing wrong with that.