CHICAGO (AP) — Scientists from Illinois have found a rare, 600-year-old Chinese coin on the Kenyan island of Manda.

The Field Museum in Chicago announced the find Wednesday. The joint expedition was led by Chapurukha Kusimba of the museum and Sloan Williams of the University of Illinois-Chicago. Researchers say the coin proves trade existed between China and eastern Africa decades before European explorers set sail.

The coin is made of copper and silver. It has a square hole in the center so it could be worn on a belt. Scientists say it was issued by Emperor Yongle of China and his name is written on the coin.