Quoridor

Quoridor is an abstract strategy board game for two (or four) players. Each player has a pawn that starts at the center of their side of a 9x9 grid. The goal is to be the first to reach the opposite side. On each turn, a player either moves their pawn one square orthogonally (not diagonally) or places a wall — a barrier that spans two cells — to impede the opponent. The critical rule is that you may never completely block an opponent's path to their goal; there must always be at least one route remaining.

Rules

1. The board is a 9x9 grid. Each player's pawn starts in the center cell of their baseline (starting row).
2. Each player has 10 walls (in a 2-player game).
3. On each turn, a player does one of two things:

• Move: Move their pawn one square horizontally or vertically (not diagonally) to an empty adjacent square. Pawns cannot pass through walls.
• Place a wall: Place a wall that covers exactly two squares of a groove between rows or columns. Walls can be horizontal or vertical.

1. Jumping: If your pawn is adjacent to the opponent's pawn, you may jump over it to the cell directly beyond (if that cell is empty and not blocked by a wall). If that cell is blocked, you may jump diagonally to either side.
2. Path Rule: A wall may not be placed if it would completely cut off any player's path to their goal row. There must always be at least one path available for every player.
3. The first player to reach any cell on the opposite side of the board wins.

Strategies

• Move-First or Wall-First: In the opening, moving your pawn forward is often more valuable than placing walls. Get ahead early, then use walls to protect your lead.
• Shortest Path Awareness: Always count the shortest path for both yourself and your opponent. Place walls that extend your opponent's path without significantly lengthening your own.
• Wall Economy: You have only 10 walls. Using them all early leaves you unable to interfere later. Save walls for critical moments when your opponent is close to winning.
• Corridor Creation: Guide your opponent into long detours using a sequence of walls that create a winding corridor. Each wall should extend their path by at least 2 moves to be efficient.
• Jumping Exploitation: Position yourself adjacent to your opponent to set up jump opportunities. A well-timed jump effectively gives you a free extra move.
• Center Control: Staying near the center of the board keeps your options open. Edge positions restrict your mobility and make you more vulnerable to wall placements.

Quoridor was invented by Mirko Marchesi, an Italian game designer, and published in 1997 by Gigamic, the French board game company known for abstract strategy games. The game was designed to be elegant and accessible — with simple rules that create deep strategic gameplay.

Quoridor won the Mensa Select award in 1997, recognizing it as a game that challenges and stimulates the mind. The award helped establish its reputation as a premium abstract strategy game. The game also received a nomination for the Spiel des Jahres (German Game of the Year), one of the most prestigious awards in the board game industry.

The game is related to earlier wall-placement games. The most notable predecessor is Blockade, designed by Philip Slater and published by Lakeside Games in 1975. Blockade used a similar concept of moving pawns and placing walls on a grid, though with different board size and wall rules. Marchesi refined the concept with the 9x9 board, the path guarantee rule, and the elegant 10-wall limit that created a more balanced and strategic experience.

Quoridor has been the subject of AI research due to its interesting combination of movement and board modification. The branching factor is high (many possible wall placements per turn), making it a non-trivial challenge for game-playing algorithms. The game has been implemented in numerous digital versions and is a popular choice for programming assignments in AI courses. Competitive Quoridor communities exist online, and the game is regularly featured at abstract game tournaments.