• Board
• Objective
• Definitions
• Play
• Komi and button
• Variants
• External Links

Catena is played on a hexagonal board with six cells per side. Larger boards, up to ten cells per side, can be used for a deeper game.

There are two players: Black and White. Each player has an unlimited supply of stones of their color.

The goal of the game is to have a higher score than the opponent when no more stones can be placed.

A group consists of all stones that are connected to each other through adjacent stones, regardless of their color.

A singleton is a group of one stone.

A ribbon is a group that forms a single chain: every stone is adjacent to at most two other stones, and the chain does not close into a ring. A singleton is also a ribbon.

A ribbon is called bounded if it cannot be extended, i.e. if no stone can be placed next to it.

Each of these groups is a ribbon: a straight one, a bent one and a singleton.		None of these groups is a ribbon. In the first one, the stone on D4 is adjacent to three stones. In the other two, every stone is adjacent to two stones.

The game begins with an empty board. The button (see below) is placed next to it.

Players move alternately, starting with Black.

On each turn a player performs one of the following actions:

• Place a stone of their color on an empty cell, provided that every group remains a ribbon.
• Take the button, provided that neither player has taken it yet.

Placement

After a placement, the group containing the new stone must be a ribbon. The new stone can start a new ribbon (a new singleton), extend an existing ribbon or join two existing ribbons into one, but it can never create a branch or close a ring. The colors of the stones do not matter.

The diagram below shows examples of legal and illegal placements for either player:

• B5 is legal: the new stone extends the ribbon C5-E5.
• F5 is legal: the new stone joins the ribbons C5-E5 and G5-H7 into one.
• D6 is illegal: with C5 and D5, it would close a ring of three stones.
• G6 is illegal: it would be adjacent to three stones.
• I6 is illegal: it would create a branch at H6.

A placement may create newly bounded ribbons in two ways: either by extending an existing ribbon to the point where it cannot grow anymore, or by placing a stone near the end of an existing ribbon and thereby blocking every way it could still grow.

Claiming

After a stone is placed, every ribbon that has just become bounded is claimed by the player with more stones in it: all opponent's stones in this ribbon are replaced with stones of that player's color. Note that a player's own placement may result in their stones being replaced with the opponent's stones: it does not matter who made the bounding move, only who has the majority. If a newly bounded ribbon has the same number of stones of each color, it is claimed by the opponent of the player who made the bounding move.

A bounded ribbon never changes again.

Below is an example of a claim:

Before: B1, B2 and B6 are illegal, so B7 is the only cell where the outlined ribbon can grow. White places a stone on C8.		After: C8 extends the ribbon C7-E7, so B7 is now adjacent to three stones and illegal. The outlined ribbon is bounded. White has four of its six stones, so White claims it.

End of the game

The game ends when no more stones can be placed. At this point every ribbon is bounded and claimed.

A player's score is the number of stones of their color on the board, plus half a point if they have taken the button, plus the value of komi in the case of White player. The player with the higher score wins the game.

The komi is the whole number of points which is added to White's score at the end of the game as a compensation for playing second. Before the game starts, the first player chooses the value of komi from 0 to 15, and then the second player chooses which color they want to play with.

The button is a special token which is used to avoid ties. At the end of the game, the player who has taken the button gets an extra half point in their score. If the button is not taken before the end of the game, it is given to the player who did not place the last stone.

The game type and the scoring type are game options.

Game type

• Komi: the rules described above.
• No komi: the first player places a Black stone. The second player then chooses which color they want to play with. There is no komi.
• Double placement: the first player plays with Black stones, and colors cannot be swapped. There is no komi and no button. Black places one stone on the first turn, and every later turn places two stones, one after the other. Ribbons are claimed after each stone. When the player to move cannot place two stones, the game ends. Every ribbon that is not bounded yet is then claimed by the player with more stones in it. If such a ribbon has the same number of stones of each color, it is claimed by the opponent of the player who made the last move.

Scoring type

• Standard scoring: the score described above.
• Longest ribbon: at the end of the game, pairs of ribbons of the same length and opposite colors are removed until no such pair remains. The owner of the longest remaining ribbon wins. If no ribbon remains, the player who has the button wins. The komi, from 0 to 15, is added to the length of White's longest ribbon (one of them, if several have the same length) before the pairs are removed.
• Square score: each ribbon adds the square of its number of stones to its owner's score. The komi, from 0 to 1000, and the button are added as in standard scoring.

• Catena on BoardGameGeek.