On the Ghanaian coast where many of the slaves set off on their journeys of no return, the so-called slave castles are a vivid reminder of the barbarity of the practice.
In 1997, UNESCO established 23 August as International Day for the Remembrance of the Slave Trade and its Abolition.
The day was inspired by events of the night of August 22 to 23, 1791.
On this night, men and women, torn from Africa and sold into slavery, revolted against the slave system in present-day Haiti and the Dominican Republic, demanding freedom and independence.
The uprising set forth events that eventually led to the abolition of the slave trade. Haiti's independence in 1804 is also the only one born out of a successful slave uprising.
The day aims to memorialize millions of people who were the victims of the trans-Atlantic slave trade – one of the most frightening chapters in the history of humankind.
Each year the UN invites people all over the world, including educators, students, and artists, to organize events that center on the theme of this day.
"Once and for all, it is time to abolish human exploitation and to recognize the equal and unconditional dignity of each and every individual on Earth," said UNESCO director-general Audrey Azoulay in a statement.