Ordo
An abstract board game for 2 players by Dieter Stein

Material

Terminology

“Group”

Orthogonally or diagonally connected group of all pieces of a player.

Figure 1Pieces of the same color must be always connected.

“Singleton”

A single piece (in contrast to an → ordo).

“Ordo”

Orthogonally (in a straight horizontal or vertical line) connected group of two or more pieces of a player.

Figure 2Ordos are always orthogonally connected.

“Home row”

Nearest row on the board seen from a player’s perspective.

Figure 3Home rows

Setup

Pieces are setup as shown in the following figure.

Figure 4Initial setup

Objective

Players move their pieces trying to reach the opponent’s home row.

Play

Players choose their colors and take a seat on their side of the board. White starts, then players take turns making a move. They may not pass.

Connection

Throughout the game, after a player’s move, all pieces of said player must be connected in one sole group.

Moves and Captures

There are two possible ways to move the pieces: singleton moves and ordo moves.

Singleton Move

A singleton can move forward or sideways, orthogonally or diagonally in a straight line any number of empty squares. It may end the move in an empty square or a square occupied by an opponent’s piece, which is then captured and removed from the board.

Figure 5A singleton moves forward or sideways. Additionally, backward moves are allowed in reconnection moves (see below).

Figure 6The marked piece has 5 possible moves. Moving one space ahead and further moves to the left are not allowed as they would split the group.

Ordo Moves

A group of more than one piece, which is connected in a straight horizontal or vertical line (a so called ordo), can move side by side any number of empty squares. An ordo may only move orthogonally (not diagonally) forward (if it is horizontally aligned) or sideways (if it is vertically aligned), the same number of squares. It may not capture.

Figure 7Ordo moves for White.

Figure 8Invalid: Both pieces must move the same number of squares.

Figure 9Invalid: Pieces may not go in single file.

Disconnection

If a player’s group is disconnected because of a capture move by the opponent, that player must move (or capture) such that the group is connected again. If no such move is possible, the game is lost immediately.

Normally, pieces move forward or sideways. In case of a split group (and only then), pieces may also move backwards. This is also true for ordo moves.

Figure 10Backward directions are only allowed for reconnection moves.

Figure 11Backward reconnection ordo move.

End of the Game

The main goal of the game is to place (at least) one piece on the opponent’s home row.

Figure 12White wins the game.

Also, players lose a game

Remark

If a player has only one piece left, said piece is still considered a group!