Almost every abstract game that asks you to line up five markers on a grid traces back, directly or by family
resemblance, to a single ancient idea: get five of your stones in a row before the other player does. That idea is
Gomoku, and its simplicity has made it one of the most reinvented games in the world — handicapped, captured,
doubled,
rotated, digitized, and eventually solved outright.
An old idea on a borrowed board
Gomoku was never given a board of its own. It borrowed the Go board — nineteen lines by nineteen, or the smaller
fifteen-by-fifteen grid — and the same black and white stones, and simply changed the goal. The names it collected
as it
spread say a lot about its reach: in Japan it was gomoku-narabe, "five stones in a row"; in China
wuziqi; in Korea omok. When it reached Britain in the nineteenth century it was called
"Go
Bang," most likely a corruption of goban, the Japanese word for the Go board itself. The rules are
learnable
in a sentence, which is exactly why the game has traveled so far and mutated so often.
Renju: the game grows up
A game that simple has a problem hiding inside it: whoever moves first has a real advantage. Serious players noticed
early. In 1899, Japanese players formalizing tournament play renamed the competitive version Renju
— "five pearls in a row" — and began layering handicaps onto the first player to rebalance the game.
Those handicaps became Renju's signature: the opening player is forbidden from making certain overwhelming
shapes —
notably the double-three and double-four — and cannot win with an overline of six or more, restrictions the second
player never faces.
A capturing offshoot appeared too. Ninuki-renju added the ability to remove a bracketed pair of
enemy stones, and had its own organization in Japan from 1923 until 1940 — a branch that would later
cross the Pacific and become a hit under a different name.
The first-player problem — and a proof
For most of the twentieth century, the claim that the first player could always win free-style Gomoku was folklore:
Japanese professionals had asserted for decades that five-in-a-row on a fifteen-by-fifteen board
was
a won game for whoever moved first, but no one had ever substantiated it with a full tree of variations or a
program. The proof finally arrived from computer science. L. Victor Allis, with a
program
named Victoria, established the game-theoretic value of two common Gomoku variants, and showed that Victoria is
bound to win against any optimal defense when it moves first. The techniques he introduced to do it —
threat-space search and proof-number search — are still foundational to how five-in-a-row
engines are written today. (The game is also hard in a formal sense: Reisch proved in 1980 that
Gomoku, as Gobang, is PSPACE-complete.)
That result is the reason competitive Gomoku can't just be played "raw." Every serious version of the
game is,
at
heart,
an answer to the first-player problem.
The family tree
Mathematicians gave the whole clan a name. Gomoku belongs to the m,n,k-games — a generalization
to a
board of m by n intersections where a line of k wins; ordinary tic-tac-toe is just the tiny (3, 3, 3)
sibling, and Gomoku the (15, 15, 5) or (19, 19, 5) grown-up. A further generalization, the
Connect(m,n,k,p,q) games, adds the number of stones each side places per turn and the number the first player
places
on the opening move — machinery that turns out to be exactly what one modern descendant needed.
Reinventions
Pente — five in a row, with teeth. The most successful Western descendant was born in an unlikely place.
Gary Gabrel invented Pente in 1977 while working as a dishwasher at the original Hideaway Pizza
in
Stillwater, Oklahoma, where customers played it on the checkerboard tablecloths while they waited.
Pente — Greek for "five" — is based on ninuki-renju, keeps the five-in-a-row goal, allows
captures,
and
adds a new opening rule. You win either by making five in a row or by capturing
five
pairs
of your opponent's stones through custodial capture, sandwiching an adjacent pair between two of your
own. It
became a genuine hit: Games Magazine named it a Hall of Fame winner in 1991, and after Hasbro ceased distribution in
1993, Winning Moves revived it in 2004.
Connect6 — two stones at a time. Where Renju handicaps the first player and Pente lets the second player fight
back
with captures, Connect6 balances the game through sheer arithmetic. Introduced in 2003 by
Professor
I-Chen Wu at National Chiao Tung University in Taiwan, it has each side place two stones per turn — except the
first
player, who places only one on the opening move — and asks for six in a row instead of five. Because each
player is always exactly one stone behind after completing a turn, the first-move advantage that
plagues Gomoku and Connect Four largely evaporates, quite possibly needing no further compensation at
all. It is a direct member of the formal family — Connect6 is precisely Connect(m, n, 6, 2, 1) —
and it was presented to the academic world at Advances in Computer Games in 2005.
Pentago — five in a row, then spin. The most physically inventive descendant adds a moving board. Invented by
Tomas Flodén, Pentago is played on a six-by-six board split into four three-by-three
quadrants; on each turn you place a marble and then rotate one quadrant ninety degrees, and you win with five in
a
row before or after the twist. Released in Sweden in 2005, it is five-in-a-row married to
a rotating board. Its designers are explicit about the lineage: Pentago is not related
to
Go — it is much closer to Gomoku. And like its ancestor, it has been conquered by computers — Pentago has been
strongly solved, with the first player winning under perfect play.
The gravity cousin: Connect Four. The household name in this corner of the game world, Milton Bradley's
Connect
Four
(1974), isn't a direct child of Gomoku so much as a cousin in the broader connection-game family — four in a
row
rather
than five, with gravity pulling every piece to the bottom of its column. It shares Gomoku's deepest trait,
though:
like Gomoku, Connect Four has been proven to hand the first player a large advantage, and
it too
has been solved as a first-player win.
Gomoku goes digital
The game made the jump to screens almost as soon as there were screens to make it to. Nintendo
developed and published Gomoku Narabe Renju for the Family Computer, releasing it on August 27, 1983 —
literally the fourth game released for the Famicom, launched the same day as Nintendo's
Mahjong.
It let players pick from three difficulty levels and choose between a computer opponent and a
second
human — a structure that, four decades on, is still the sensible shape for a Gomoku app.
As a computing problem, five-in-a-row became a favorite proving ground.The Computer Olympiad
featured Gomoku beginning in 1989 but dropped it after 1993 once it was effectively solved; the Renju World
Computer
Championship ran from 1991 to 2004; and the Gomocup engine tournament has run annually since 2000. Modern
approaches have followed AI's larger arc: Gomoku's simple rules and deep strategy make
it
an
excellent testbed, and recent agents apply everything from Allis's threat-space and proof-number search to
AlphaZero-style deep reinforcement learning. Competitive human play, meanwhile, settled on its own
elegant
fix — the Swap2 opening, in which the first player lays three stones and the opponent chooses which side to take or
reshapes the position and hands the choice back, a rule derived from Renju's swap and first
seen
online at kurnik.org.
The through-line
It is a strange kind of durability. A rule a child can grasp in one sentence has been, over a century and more,
given
handicaps (Renju), given claws (Pente), given a second stone (Connect6), given a rotating floor (Pentago), packed
into
one of the first home-console cartridges, and pursued all the way to a mathematical solution. Each reinvention is
really
an argument with the same stubborn fact — that moving first is worth too much — and each argument produced a new
game.
The tools haven't drifted far from the source, either. A modern Gomoku engine still works the way Allis taught
it
to:
prune the board to the squares near existing stones, score the position by its threat shapes — open threes, fours,
the
unstoppable open four — and search a few moves deep for the double threat that can't be answered. Which is to
say
that
the newest five-in-a-row program and the oldest folk game on the Go board are, underneath, playing exactly the same
game.
