Renju

Renju is a formalized, professional version of the ancient game of Gomoku, which originated in China and spread to Japan by the late 19th century. The transition from the informal game of five-in-a-row to Renju was driven by the discovery that the first player held an insurmountable advantage. To balance the play, specific constraints were introduced for the black stones, such as forbidding double-three, double-four, and overline patterns.

The standardization of Renju is largely credited to the Renju Kyokai, the Japanese association established in the early 20th century to govern professional play. The board design typically features a 15x15 grid, a reduction from the traditional 19x19 Go board, to better accommodate the strategic complexity of the game. It was conceived as a test of logical depth and rapid calculation, and it remains a respected intellectual pursuit in East Asia and parts of Europe today.