Kingdom of Ife: Sculptures from West Africa

Once variously considered products of a 'Lost Atlantis', or an 'African Donatello', the copper-alloy heads that are the stars of this touring exhibition (made between the twelfth and fifteenth centuries in what is now Nigeria), have been the subject of much bartering - both cultural and literal. Worldwide interest was sparked by German ethnologist Leo Frobenius's 1910 'discovery' of the so-called 'Olukon' head (since reckoned a twentieth-century copy, but co-opted as something of a pan-African mascot, appearing on stamps and hairdressing salons). But it was the 'Wunmonije' heads, unearthed in 1938, that prompted the more fanciful speculation about the society that created them.

Deprived, in most cases, of the paint and beading that once decorated them, as well as their crowns and caste trappings (not to mention their bodies), these heads, with their subtle modelling and delicate facial striations, are now testament to the artistic sophistication of Ife rather than the power its ruling elite wielded in life. Whether these works represent men or gods, they have transcended their original culture through an aesthetic ambition that is universally recognisable and staggering.

A large copper mask, known as 'Obalufon', covers the wearer's whole head, yet its presumed symbolic significance now seems less important than the impression it conveys of benign composure. If anything, it suggests that it would subordinate any wearer to the perfection of the artist's vision: the mask's eyes are full, limpid, the lips sensitive, but the wearer must make do with tiny crescent slits to peer through and a slot mouth, as though the piece is rationing both sensory experience and expression.

In this hierarchy of materials - Ife had no metal deposits, so all the copper and tin had to be expensively traded - it is almost a relief to get to grips with the earthier (literally) works in stone and terracotta that make up the remainder of the show. After all that transcendent beauty, these more humble pieces have a compelling immediacy: a crude granite mudfish, like a huge wafer of soap with tiny iron hobnail eyes; a small, vividly worked terracotta head of an old man who seems to be almost audibly spluttering for attention in the midst of all this regal placidity.

Pop-eyed gagged heads and a figure of a man with roped ankles and giant swollen gonads suggest that everyday life in Ife was not all cultured sophistication. There are chameleons and owls, domestic animals and livestock - reminders that far from being some lost civilization, Ife continues to exist where these works were produced - an unbroken thousand years of history.

This show is not perfect: the BM still lacks a successful temporary exhibition space, and the works feel more like curiosities than they should in this room above the Great Court, but for the jolt of pure artistic achievement it delivers, it would be hard to regard it as anything less than a triumph