Jonathan Jones, in the Guardian (6-30-05):

... The slave trade was two centuries ago. But here in this castle [ Cape Coast Castle in Ghana, west Africa] it remains more immediate than anywhere else on earth. The enlightened 18th-century Britons who drank coffee and tea with sugar harvested by African slaves on Caribbean plantations couldn't see the violence beneath the sweetness, until campaigners put images before them: "Am I not a man and a brother?" asks the chained slave engraved by the abolitionist Josiah Wedgwood. Even now, making global economics visible is difficult. Is it possible to see what cannot easily be represented - the hidden structures of exploitation?

With slavery, which is history, you can try to do this. You can map the hideous trade simply by visiting a transatlantic triangle of museums. I didn't quite complete the circuit by going to, say, Monticello in Virginia, where you can see the slave quarters that disfigure the Palladian mansion of American founding father Thomas Jefferson. But I did compare slavery exhibits in west Africa and the north atlantic trading port of Liverpool.

In the slavery section at the Merseyside Maritime Museum you can see the log book of the Unity, a Liverpool ship that left the Mersey in 1769, bound for West Africa, where it moored beside Cape Coast Castle before heading for Jamaica, returning to Liverpool in May 1771. This was the triangular trade. When it set sail from Liverpool, the Unity would have been loaded with iron, brass and copper, silk, guns and textiles, to trade with African slavers who brought prisoners of war, criminals, or simply kidnapped children (like the Ibo boy Olaudah Equiano, later to publish his memoirs in 1789), to the coast to sell to the Europeans. At Cape Coast Castle the Unity's captain made the trade, picking out slaves - primarily young men. Then the ship set sail for Jamaica, where its human cargo was again auctioned. On the leg, back to Liverpool, the same ships carried the sugar and tobacco to which the home market was addicted.

Slavery, as the historian Niall Ferguson points out, "made overwhelming sense as an economic proposition". It made sense, especially, to the port of Liverpool, from where 33 ships a year were setting out on the triangular route by 1740. Today you can see the last echoes of Liverpool's once vast Atlantic commerce in a container ship gliding out of the Mersey past the Albert Dock.

It's a noble thing that this city preserves the memory not just of its past triumphs but its past crimes. Its slavery exhibit is centred on a re-creation of the cramped, dark quarters in which up to 13 million Africans made the Atlantic crossing. Cleverly designed so that for a second you can't see the entrances and are completely immersed in its ghostly shadows, the reconstruction works. It scares you.

Slavery is gothic. In Liverpool, they have a rusty 18th-century device for disciplining slaves: a collar with a spike forcing the head into painful uprightness. Was this the Enlightenment? It's understandable that the anger of the curators intrudes clumsily at times. "During the 17th century," declaims one of the many, many wall texts, "Europeans developed views of their own racial superiority for reasons of self-interest." It's true, but nothing can be stated that baldly without replacing history with ideology. That in turn invites scepticism in any but the most passive visitor.

The same danger is courted by downplaying the involvement of Africans in the slave trade, not to mention Arab traders who traversed the Sahara in the middle ages. It's unnecessary, because the facts speak for themselves. It was neither Africans nor Arabs who came up with the idea of compressing a human cargo into ship holds to sail the wide Atlantic, but Europeans. It was a British sea captain who invented the refinement of this commerce that finally brought its obscenity to light, when in 1781 the Liverpool ship the Zong threw more than 100 sick slaves overboard for the insurance. With facts like these you can tone down the rhetoric.

This is why, museologically speaking, I found that Ghana has done a better job than Merseyside. You can't avoid the history of slavery here, on what was once called by Europeans the "gold coast". The coast is decorated with a string of forts that were used to hold slaves and protect moorings, with bastions and guns to fight off African neighbours as well as European rivals. The presidential residence in Accra is itself a former slaving castle; the last British governor, who lived here until independence in 1957, claimed it was haunted by the fettered dead....

The slave trade died in the 19th century, and it would be impossible to prove it somehow caused the poverty of millions of Africans today. Polls suggest most of us don't even see later colonialism as a factor. History, memory, is so easy to obliterate. That's why these museums, in Ghana and Liverpool, matter. But the most telling thing is their contrasting surroundings. The road from Accra to Cape Coast, for all the natural beauty, is a dismal journey past scenes of medieval deprivation so universal it boggles the mind. Liverpool is nothing like Britain's most affluent city. But the walk from the Albert Dock takes you past all the banal luxuries we take for granted, just as the British once took it for granted that African lives were worth less than sugar.