One would think that slavery belongs in the history books, but in 2017, many Nigerians, Senegalese and Gambians who are on their way to Europe are still bought and sold just like in the 16th century.

According to the International Organisation for Migration, IOM they are traded for between 75,000 and 200, 000 Naira and held on average for two or three months.

They are traded in what they call slave markets before being held for ransom, forced labour or sexual exploitation.

A Pulitzer Prize-winning photographer, Narciso Contreras who also spoke to Reuters on the matter, Wednesday said that Libya has become a modern-day slave market.

"What I found is that it's a slave market, it's like an industry but the world is looking at Libya as a transit country," Contreras told the Thomson Reuters Foundation.

Libya was a rising star in Africa until the fall of Muammar Gaddafi in 2011.

It has since descended into lawlessness with governments at every corner and several armed groups competing for land and resources; and large weapons and people-smuggling networks operating with impunity.

Contreras met two West African migrants who had been held as slaves. One of the slaves' owners ran an immigration detention centre and the second was a local militia leader, he said.

"These seemed to be typical stories of the impunity you find in Libya," said Mexican-born Contreras, who won the Pulitzer Prize in 2013 for his work in Syria.

Contreras also took pictures of the detention centres where migrants endure overcrowding, lack of sanitation and beatings.

"There is no humanity in these places," said Contreras.