The Kalacakra is a well-known Buddhist image that illustrates important Buddhist teachings.  The circle represents the cycle of birth and rebirth, and the images inside illustrate the forces that keep beings trapped in this cycle. 

The circle is held by Kala (in Sanskrit, both "time" and "death"), who personifies the forces of death and destruction. 

Outside the circle are two beings who are outside this cycle--on the right,  Shakyamuni, the historical Buddha (who discovered the cause of rebirth and the path to liberation), and on the left a celestial Bodhisattva. 

The concentric circles convey different Buddhist teachings: 

1. The two inner circles portray the emotional forces that bind human beings, and the course of negative and positive karma. 

22. The six sections in the larger middle circle portray the  six realms of existence (clockwise from top--gods, asuras, animals, hells, ghosts, and human beings). Of these, the human realm is considered the best, but each realm has a Buddha to bring teaching to its inhabitants.

3. The outermost ring illustrates the  12 stages in the Buddhist causal chain leading to rebirth

("Dependant Origination /pratityasamutpada)