African nations launched a design contest for a $500-million memorial to slaves to be erected near the spot from which millions of Africans were shipped abroad. At a U.N. ceremony presided over by President Moussa Traore of Mali, project official Eugene Jackson said the memorial will be a symbol of unity of African slave descendants worldwide. Part of the project will be a monument on Goree Island, near Dakar, Senegal. The island and a nearby cape were ports for 19th-Century French, Dutch, Portuguese and British slave traders. An estimated 20 million Africans were shipped to the West Indies and the Americas.