Bronze, at Royal Academy, Seven magazine review A local Mafia boss's attempts to steal it were foiled, and now this venerably ancient work of art is one of the prize possessions of modern Sicily. But for the present it occupies the main octagonal gallery of the Royal Academy: a show-stopping prelude to a jaw-dropping exhibition. Bronze is an improbably old-fashioned, awe-inspiring blockbuster of a show. The idea behind it is straightforward: bring together 150 of the world's finest sculptures in bronze, from a multitude of cultures and societies, ranging from ancient China to 19th-century Indonesia, from medieval England to Renaissance Italy, from India at the dawn of Buddhism to America in the shadow of the Second World War. The chief curator, David Ekserdjian, has a keen eye, a sharp mind and self-evidently extraordinary powers of persuasion, to judge by the multitude of seemingly unlendable treasures he has managed to obtain from all four corners of the earth. The contents of this cornucopia have been arranged thematically, under headings such as "Figures," "Animals," "Gods," "Heads" etc. The resulting chronological confusion is discombobulating, exhilarating and educational by turns. The show is best approached as a modern wunderkammer, a labyrinth of theatrically darkened galleries, filled with wonders. Leaving Dancing Satyr behind, the visitor passes into a room teeming with other, equally beguiling forms of imagined life. There are solemn Benin bronzes from Nigeria. There is the poignantly attenuated Etruscan votive figure known as the Ombra della Sera (the "Evening Shadow") a man on the brink of his own vanishing - a work so repeatedly plagiarised by that petit-maître of existential Paris, Alberto Giacometti, that modern viewers may be surprised to find that it was created nearly 2,000 years before Giacometti was even born. There is Donatello's ecstatic Putto with Tambourine, coiled like a spring, alive with sheer joy - a sculpture rescued by the connoisseur Wilhelm von Bode from a junk shop near the Portobello Road, and now one of the treasures of Berlin. Somehow or other, the authorities at Orsanmichele in Florence have been prevailed upon to loan one of the great bronze statues created for its niches by Lorenzo Ghiberti. His St Stephen, of 1425-9, faces an equally impressive Roman bronze of 41-54 AD, from the Archaeological Museum in Naples, depicting one Lucius Mammius Maximus, formerly of Herculaneum. How thoroughly un-Renaissance, how stiffly medieval Ghiberti's figure seems, confronted with the relaxed naturalism of the actual antiquity it was once said to revive. An even more remarkable loan from Florence is to be found nearby: three monumental figures, embodying St John the Baptist Preaching to a Levite and a Pharisee, which until recently stood above the north door of the city's baptistry. Recently restored, they can now be seen at ground level for the first time in centuries. The group has traditionally been attributed to Francesco Rustici, an intimate member of the circle of Leonardo da Vinci, although Leonardo's early biographer, Giorgio Vasari, stated that "some believe, without knowing it for a fact, that Leonardo worked on it with his own hand..." Close inspection shows little affinity with the known works of Rustici and startling similarities with the work of Leonardo - particularly in the faces and gestures of St John and the Pharisee, which seem uncannily close both to Leonardo's St Anne, and to various of his sketches now in Windsor Castle. A new monumental sculpture by Leonardo da Vinci? It really is more than likely. Ekserdjian has an eye for new discoveries, but also a knack for seeking out overlooked marvels in supposedly familiar places. The medieval sanctuary ring, in the Cathedral Museum at Durham, is not exactly well known. But it is a truly extraordinary object, a snarling head with the unexpected reek of an Aztec altar or an American Indian totem pole: what a convulsively superstitious tribe the English once were. Just as startling is the Portrait Head of King Seuthes III, a masterpiece of Thracian art from the fourth century BC that was recently unearthed in Bulgaria. The Pygmalion portrait of a thickly bearded autocrat, with pensive, troubled, living eyes, this is an almost inconceivably skilful work of art. It looks like it ought to have been created by some bronze-working prodigy at one of the great courts of Baroque Europe. To discover it was made thousands of years earlier, in a supposed backwater of the antique world, beggars belief. There are altogether too many wonders, in this particular wunderkammer, to begin to enumerate them all. Unlike marble or wood, the unyielding material properties of which necessarily confine the sculptor's imagination, bronze is shape-shiftingly adaptable, and therefore peculiarly hospitable to the free play of imagination. Ultimately, it is that freedom which is so generously celebrated here, across continents and across millennia. Is there a moral to it all? Maybe just that art does not progress; it merely changes. To Dec 9; www.royalacademy.org.uk