After the 1912 Stockholm Games—the first Games featuring athletes from all five inhabited parts of the world—a design of five interlocked rings, drawn and colored by hand, appeared at the top of a letter Coubertin sent to a colleague. Coubertin used his ring design as the emblem of the IOC’s 20th anniversary celebration in 1914. A year later, it became the official Olympic symbol.
The rings were to be used on flags and signage at the 1916 Games, but those games were cancelled because of the ongoing World War. The rings made a belated debut at the 1920 Games in Antwerp, Belgium.
Read more about the rings, including how they were confused for an ancient symbol, what the colors mean, and the rules for their use at mental_floss. Link
(Image credit: Flickr user paul_appleyard)