The tradition of minting coins started in ancient Greece. The images of emperors and famous rulers have been encrypted on obverse since ancient times. The reverse sides of the world coins remained hallow. It was until the tradition of incrusting different great civic symbols or important natural monuments appeared in 8^th century B.C. in ancient Greece. The city-state was the first greatest civic symbol to appear on the reverse.

I found this article on dig4coins.com and the tradition is really beautiful, that has many historical events.