Europeans also figure prominently in Gambian history because the River Gambia is navigable deep into the continent, a geographic feature that made this area one of the most profitable sites for the slave trade from the 15th through the 17th centuries. (It also made it strategic to the halt of this trade once it was outlawed in the 19th century.) Some of this history was popularised in the Alex Haley book and TV series ''Roots'', which was set in the Gambia.