Decline in the slave trade in the 19th century resulted in an economic crisis. Cape Verde's early prosperity slowly vanished. However, the islands' position astride mid-Atlantic shipping lanes made Cape Verde an ideal location for re-supplying ships. Because of its excellent harbour, the city of Mindelo, located on the island of São Vicente, became an important commercial centre during the 19th century. Diplomat Edmund Roberts visited Cape Verde in 1832. Cape Verde was the first stop of Charles Darwin's voyage with  in 1832.