This African art is heads above the rest

Bronze Ife heads amazed our critic in a dingy Nigerian museum. Now on show in London, they will change your view of African art

A glorious display of Ife sculpture has arrived at the British Museum. Nobody - and I mean nobody - in Britain should miss it. Why? Because it changes our understanding of civilisation. Because it rewrites the story of art. Because it is a once-in-a-lifetime revolutionary event. If none of those is a big enough reason for you, then go along merely to enjoy some of the most graceful and lovely sculpture ever made. Trust me. You need to see this one.

For me, Ife is a personal cause. Three years ago, I went to view for myself where this thoroughly surprising African art had originated. It was the middle of the rains, so the drive across Nigeria was terrifying and seemingly eternal. At the end of the bumping and skidding, modern Ife was a disappointment: grubby and pint-sized. The museum devoted to its ancient sculpture was, frankly, pitiful. No lights. Chameleons clambering over the exhibits. Rain dripping off the roof into the displays.

The biggest shock, though, was walking into the gallery in which the life-sized Ife heads were supposed to be found. Because there weren't any. On show instead was a row of empty plinths. The director, a visibly worn-down chappie, explained they had been stolen. Those that had not been stolen had been taken by Lagos. So there were only a couple of heads left. Over there. In that corner.

I leant into the darkness to inspect one of the survivors, and bang: someone hit me over the head with the hammer of ecstasy. It was only a bronze head, weakly displayed in a pitiful museum. Nothing about the setting showed it off to any advantage. But God, how beautiful it was. How skilled and exceptional. How elegant. How unexpected. How revolutionary. If all the sculpture in the world had this calibre of impact, then all our galleries would be a-wobble with human jelly.

Ife was a wealthy city-state that flourished in what is now western Nigeria between the 12th and 15th centuries. Arising in mysterious circumstances, it decayed mysteriously, too, and absurdly little information has come down to us about its past. Nobody in the West even knew they made art here until 1910, when a German archeologist, Leo Frobenius, spent three weeks in the region collecting objects. His dig was ridiculously short, but the discoveries he made were monumental. When he returned to Europe and showed off what he had found in Ife, nobody would believe him. You, too, might have difficulty as you wander among the dramatic array of artefacts gathered in this utterly surprising African display: the full-size human figures cast in bronze; the delightful terracotta likenesses of animals; above all, the ravishingly beautiful heads. Staring ahead with unwavering calmness, perfectly proportioned, elegantly cast, these exquisite portrait sculptures feel more like the opposite of African art than superior additions to its canon.

Imagine the shock when, instead of grimacing witch-doctor masks and bone-tied voodoo objects, these naturalistic human evocations began coming out of the ground. Everything we thought we knew about African art was wrong. Small wonder the first explanation offered by archeologists for the art of Ife was that it must have been made by a lost tribe of Greeks who had somehow blundered across the Sahara. Frobenius himself claimed it was created by the citizens of Atlantis. Somebody, anybody, whoever. But not Africans.

We now know that Ife did indeed bloom three-quarters of a millennium ago. While we were blundering through the gloom of our Middle Ages, carving gargoyles and lurching gothically from sin to sin, these enlightened African progressives were developing a humanistic sculptural tradition that was as technically accomplished as it was aesthetically stunning. Using a complicated lost-wax process that was hugely difficult to get right, casting life-size bronze heads to an immaculate finish, Ife's sculptors repeated their immense creative achievement again and again.

The show begins and ends with impressive clusters of these haunting faces. The head I saw in Ife is here. It presents a young warrior of irreducible nobility. As with most Ife heads, the warrior's face is covered with a dense network of lines that probably represent a set of tribal striations incised into the skin. Their effect, though, is never one of fierceness or bellicosity. Instead, the insistent patterns seem to bring an unshakable elegance to these taut, unwrinkled faces. The final effect is always of deep composure.

Nobody is sure how the Ife heads were used. A few may have been worn as masks. Most seem to have been made to stand on altars at times of worship. Interestingly, each one is different enough to suggest that a degree of portraiture was intended. The show explains that, according to the Yoruba creation myth, Ife was actually where the world began: the wellspring of all mankind. Thus, whatever it was that led to the making of the Ife heads carried with it a momentous civilisational clout. And it shows.

The heads are joined in this twilit display by rarer attempts to produce full-size figures. These are, if anything, even more impressive. A late-13th-century sculpture from Tada, about 120 miles from Ife, shows a delightfully plump seated deity, so calm and rounded, you might easily suspect him of having Buddhist origins. He was cast from almost pure copper, a fiendishly difficult process that only the most sophisticated sculptural societies would ever attempt.

While the coppery bronzes fill you with awe, the bits and pieces of terracotta head and figure that crowd the centre of the show fill you with restless fascination. That, at least, is what they did to me. Terra-cotta, which is basically baked earth, is such a fragile material that you would never suspect it of surviving for long in the Nigerian underground. Yet some of this show's most intriguing sights are, indeed, terracotta survivors: a delicate chameleon perched on a boulder captures exactly their darting movement; a grimacing old man, realistically observed, seems to be suffering from a disfiguring facial illness; a full-length figure, with enormous roundels hanging from his loins, turns out to represent a man suffering from elephantiasis, or enlarged testicles. Whatever is actually going on here seems definitely to involve facing up sculpturally to humanity's lot.

There is obviously a long way to go before we stop knowing next to nothing about the great art of Ife, and the British Museum's recent record on African art is, alas, patchy. Ever since the Museum of Mankind closed down, there seems to have been a reluctance in these parts to tackle these crucial creative tracts. Perhaps the clamour of the Nigerians for the return of their Benin bronzes is a factor: a stone ignored is a stone unturned. But as we now know that all humanity flowed, originally, out of Africa, and that all of us are African in origin, it seems particularly important to understand African art more fully. Understand African art and you understand everyone's art.

Kingdom of Ife, British Museum, WC1, until June 6