Mauritania - a desert country on Africa's north west coast - has a history of slavery going back 800 years.
Over the last century Mauritania has made several attempts to ban slavery.
But finally, in August 2007 owning slaves became a criminal act for the first time.
Overnight, half a million people - a fifth of the country's population - were officially freed from bondage.
However many of them didn't hear the news. Without having access to broadcast media or the ability to read, and even if they had, it might not have meant much.
David Gutnick of the Canadian Broadcasting Corporation visited Nouakchott, the capital of Mauritania.
He travelled around the city - including the bustling shanty towns - and finds out more about the rigid caste system that affects all walks of life in Mauritania.
During his journey he travels with his interpretor - who helps him to meet residents in Nouakchott including teachers, religious leaders, and former slaves.
David discovers how the master/slave relationship in Mauritiania can't be easily swept aside.
First broadcast on Monday 18 May 2009
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