There's a legend that, instead of fighting an invading army, an ancient Buddhist ruler of Tibet avoided bloodshed by challenging the leader to a game of Go. Whether or not that actually happened, Go, which may have originated in China, has been a popular pastime in Asia for some 3,000 years.

At first glance, the game appears beguilingly simple. Two players -- one equipped with white stones, the other with black ones -- sit down at opposite sides of a board consisting of a basic 19-line-by-19-line grid, and take turns placing stones on the vacant intersection points. A player wins by claiming more intersections than his or her opponent and /or by surrounding and capturing more of the opponent's pieces than the opponent takes.

The tension between those two different ways of scoring, and the seemingly endless strategic and tactical options that arise, are what makes the game so appealing. While it looks easy to play, in practice, Go is so challenging that, so far, no one has been able to program a computer to play the game more skillfully than the best human masters [source: International Go Federation].