Cartagena, known since the colonial era as Cartagena de Indias, is a city and one of the major ports on the northern coast of Colombia in the Caribbean Coast Region, along the Caribbean Sea. Cartagena's past role as a link in the route to the West Indies provides it with important historical value for world exploration and preservation of heritage from the great commercial maritime routes. As a former Spanish colony, it was a key port for the export of Bolivian silver to Spain and for the import of enslaved Africans under the asiento system. It was defensible against pirate attacks in the Caribbean. The city's strategic location between the Magdalena and Sinú rivers also gave it easy access to the interior of New Granada and made it a main port for trade between Spain and its overseas empire, establishing its importance by the early 1540s.