The Cape Verde islands consist of two small (volcanic in origin) archipelagos, about 400 miles off the western coast of Africa. These once uninhabited islands were first discovered by the ancient Phoenicians, then later colonized and exploited by the Portuguese, beginning in the 15th century. In the 16th century the islands became an infamous trading center for African slaves, and eventually, an important stop for transatlantic sea traffic in the 19th century. After becoming an overseas province of Portugal in 1951, the islands gained their independence on July 5, 1975. Most of the indigenous people are descendants of African slaves, and some still speak Crioulo, a Creole dialect. The local economy depends on agriculture and limited tourism.