Sankofah - If you ever did forget and you went back to reclaim, remember it’s not a taboo.

Anyone familiar with Divine chocolate knows about the sacred language of adinkra symbols. These are a form of hieroglyphics - a visual way of communicating concepts. Adinkra symbols can be found everywhere in Ghana with one of the most important, cherished and popular being Sankofah - the bird looking backwards.

Its meaning in Twi is Sε wo werε firi na wo sankͻfa a yεn kyiri. and the English translation: If you ever did forget and you went back to reclaim, remember it’s not a taboo. This broadly translates to mean that you can only shape your future by understanding your past - looking back while moving forward.

The Ghanaian coast from Accra heading West towards Cote d'Ivoire is a UNESCO world heritage site, for the worst reason. An estimated 250 million people were captured, imprisoned, enslaved and transported from ships anchored off this coast to the Americas between the 16th and 19th centuries.

Slavery has been around forever. Civilisations like the Greeks, Egyptians and Romans built empires from the work of slaves. Prisoners of war were enslaved for a period of time and almost always had the opportunity to be freed during their own lifetimes. It took Europeans - fresh from the "Enlightenment" - which held that Europeans were uniquely cultured and clever - and the Industrial Revolution - which prioritised efficiency over human rights - to turn slavery into a unique evil. People were enslaved purely on the basis of the colour of their skin, with Africans from many different tribes and peoples thrown together in the industrialisation of the Transatlantic Slave Trade.

Of the dozens of European built forts on the Ghanaian coast, the two most important are Cape Coast Castle and Elmina. Both have the above inscription embedded in their walls. It's the first thing you see.

At Cape Coast Castle I was guided by Thomas, an extremely knowledgeable historian and tour guide. The rest of our group was made up of African and African-American people - for whom a visit to Ghana is a pilgrimage in search of the roots stolen from them. Their names, professions and families were ripped away by the brutality.

Most of us know about the middle passage, and the brutality with which enslaved people were treated once they reached the Americas but the horror stories told at the Ghanaian slave sites add another dimension. Ships would leave for the Americas roughly every two to three months, so enslaved people remained onshore for all that time in increasingly cramped conditions waiting for the ships to be ready to depart.

It's estimated that less than 20% of the people enslaved and imprisoned in the forts along the coast survived to have children - whether they perished due to the filthy conditions they were kept in before boarding the boats, on the long, cramped middle passage or after arriving in the Americas due to back breaking work, new diseases or brutal treatment. Any children they did have became the property of the people who claimed to own them in the Americas. In many cases these children were the product of rape which has always been used as a way of controlling and demeaning women. Plantation owners in the Americas abused female enslaved people, and the brutal treatment started as soon as they arrived in the forts. The governors and their men took their pick of the enslaved women - choosing their latest victim from a balcony above the women's dungeon. I saw the secret staircase where the women were forced into the Governor's bedroom. Those who refused were tied up in the hot sun as a lesson to others.

Dungeons in these forts were hideously cramped - hundreds of people crowded into a room no more than 5 metres square. Archaeoloogists have excavated the floor of the men's dungeon at Cape Coast Castle and found several inches of human waste products - faeces, blood, vomit and urine. But some places were worse than others. If an enslaved person committed a crime they were put in a small room like the one above at Elmina where I was guided by historian Frederickson. No food, water, light or air was admitted. The door was not opened until everyone inside was dead. If there were ten people in there, nobody came out. The last person had to watch his comrades die and live alongside their bodies as one by one they gasped their last breath.

These unimaginable horrors were perpetuated by Europeans - at various points Elmina and Cape Coast castle were run by Danes, Swedes, Dutch, Spanish, Portuguese, French and British colonisers. The forts were purpose built for brutality. The aim was to dehumanise the enslaved people, to break their spirit, to make them compliant. And all so that Europeans and later white North Americans could have cheap cotton, sugar and rum.

I visited Harewood House near Leeds this weekend. There is an information board at the entrance stating clearly that the house was built on the proceeds of sugar plantations in Barbados, Grenada, Jamaica and Tobago, worked by an estimated 3000 enslaved people.

Contrast the opulence of Harewood house and gardens with the conditions of the enslaved people whose unpaid labour built it. It's good that stately homes are starting to acknowledge the legacy of brutally unfair trading practices - and choosing Fairtrade refreshments in their cafes - as the National Trust has done - is part of reparations for this historic wrong.

But reparations for the wrongs done to the millions of enslaved people must go much deeper. I was privileged to visit the slave river (Ndonko Nsuo) and graveyard at Assin Manso. This sacred site - around 40km North of the coast - was the place where enslaved people took their final bath in the river before being transported to the coast. This was far from a fun, relaxing experience - they were shackled throughout, and the bath was largely to prevent them from spreading disease amongst themselves.

Assin Manso has become a site of repatriation for the remains of several hundred formerly enslaved people who died in the Americas, my expert and incredibly engaging and sensitive guide, Roland. In 1998 the bodies of two enslaved people, Madame Crystal from Jamaica and Samuel Carson from New York were reburied at Assin Manso as representatives of the millions whose fate remains unknown. Others followed including over 400 found and repatriated due to the efforts of the Prime Minister of Barbados Mia Mottley. People of African American and African Caribbean heritage are encouraged to visit and take part in a ritual of remembrance for their ancestors. For my own part Thomas gave me a 0.20 cedi coin (about 2p) and Roland encouraged me to entrust my hopes and wishes to it, casting it into the river. Of course an end to world poverty and a fairer trading system were my main wishes.

As a campaigner for fair trade I understood a little about the devastating Transatlantic Slave Trade but it's only when I was fully present in these sites, struck by the errie silence, the damp walls, the cramped darkness that I fully grasped the horrors. We must understand the past in order to build a future that works for everyone, wherever in the world they live.