Ghana's crumbling castles are a grim reminder of its slave trade past

Cape Coast Castle – now a World Heritage Site – is one of about forty forts in Ghana where slaves from as far away as Burkina Faso and Niger were imprisoned. This former slave fortress could hold about 1,500 slaves at a time before they were loaded onto ships and sold into slavery in the New World in the Americas and the Caribbean.

At Cape Coast Castle, slaves were shackled and crammed in the dank dungeons. There was no space to lie down and no sanitation, with human waste littering the floor. Slaves could spend up to three months confined in these miserable conditions before being loaded onto ships.

Male captives who revolted or were deemed insubordinate ended up in the condemned cells – a pitch-black room where slaves were left to die in the oppressive heat without water, food or daylight. Rebellious women were beaten and chained to cannon balls in the courtyard.

These now silent cannons are a reminder of the military might of the British who used Cape Coast Castle to hold slaves for 140 years. It's estimated that between the late 17th and early 19th centuries, some three million West African slaves were shipped from here.

Fort Christiansborg, also known as Osu Castle, sits in the lively township of Osu in Ghana’s capital, Accra. It was built by the Danish, who originally traded in gold, then in slaves. The slave trade was so successful that they had to expand the castle to almost four times its original dimensions.

On the seaboard side of the coastal slave castles was 'the door of no return', a portal through which the captives were lowered into boats and taken to the slaving ships anchored further out at sea. Four in 10 did not survive the tortuous voyage. Those who made it across the Atlantic alive would never set foot in their homeland again.

Erected in 1784, the crumbling ruins of Fort Prinzenstein in Keta, east of the Volta River, are a reminder of Denmark's role in the transatlantic slave trade. As the first slave-trading country to abolish the practice in 1792, Denmark's barbaric involvement in shipping an estimated 120,000 slaves to the former West Indies is often glossed over.

It is easy to walk past this nondescript building in Ghana's capital Accra for anyone not aware of its historical significance. Built by the British as a trading post in 1673, Fort James was also used to hold slaves. It has a true history of chains – it was also used as a prison until 2008.

Built in 1482, Elmina Castle on Ghana's Cape coast is the earliest European structure erected in sub-Saharan Africa. Originally Portugese, it was later captured by the Dutch, who used it as a base for the Dutch slave trade with Brazil and the Caribbean. Under the flag of the Dutch West Indies Company, around 30,000 slaves a year passed through Elmina until 1814 when the Dutch abolished slavery.