For long years, since 12nd century, the discoverers swept out the western coast of Africa. It was quite obvious that the coast went on with barren desert. Some discoverers claimed that the rest of the coast was just like this, maybe going this way to the "Hell". But some others thought that, after this barren coast, there lied a fertile and prosperous land.
This land was named "Bilad Ghana" by the Arab geographer Al Idrisi. This term had also been used by Italians and later by Portuguese. And the term evolved to "Guinea".
Today, 4 countries are called with the variations of the term Guinea (Guinea, Guinea Bissau, Equatorial Guinea and Papua New Guinea), named by western colonizers as they regarded these territories as "Bilad Ghana" - "The Land of Wealth".
"Bilad Ghana" legend was one of the strong motivations of the Portuguese sailors in the Age of Discovery.