MANDA, KENYA—A Chinese coin discovered at the Kenyan island of Manda suggests that trade existed between Africa and Asia as far back as 600 years ago. The copper and silver coin, known as a Yongle Tongbao, has a square hole punched in it and was issued during the Ming Dynasty reign of Emperor Yongle, who ruled between A.D. 1403 and 1425. The age of the coin predates the voyages of European explorers, such as Vasco de Gama, by several decades, indicating trade routes might have existed before these men set sail.