Arimaa/Introduction to Strategy/Initial Piece Placement
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| Gold has used the 99of9 setup; Silver has switched the dogs and cats. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The most popular piece setup as of July 2006 is named for the player 99of9 on arimaa.com (Toby Hudson), who first used it extensively. In the diagram at right, Gold has chosen the 99of9 setup. The elephant is placed in the center to be able to attack any part of the board. The camel is placed in the center as well, but for defensive purposes. A centralized camel can discourage the opponent from launching an elephant-horse attack on either wing. Futhermore, a centralized camel can't be pinned against the edge of the board by the opposing elephant as the first stage in taking a camel hostage; in the opening the camel is safest back and center in the midst of friends.
The gold horses are placed to occupy b3 and g3, discouraging an elephant-horse attack by Silver, but also in good position to launch an elephant-horse attack for Gold. The rabbits are mostly placed in back row for their own safety, but one is placed forward on each flank to take advantage of the benefits of rabbit advancement if the opportunity arises. Furthermore, rabbits are not placed on d1 and e1, because they can relatively easily be pulled to d2 or e2 where they get in the way of a defensive camel switching wings.
The dogs and cats seldom advance in the opening, so they are kept back as well, but cats are placed behind the traps rather than dogs so that, should Gold decide to abandon a home trap in favor of attacking, it will only cost a cat as the first defender.
At right, Silver has copied the 99of9 setup with two notable differences. First, the silver elephant is not placed directly opposite the gold elephant. If the elephants directly face each other to begin, Gold can put Silver in an awkward spot by advancing the gold elephant four squares to fence in the silver elephant. Second, Silver has placed dogs behind the home traps rather than cats. Silver will find it more difficult than Gold to abandon a home trap for an attack in the opening. In compensation, the silver dogs are slightly closer to the action in anticipation of an increasingly active role for dogs later in the game. The strategic role of cats is mostly to stop opposing rabbits from reaching goal, so they are well-placed out of the way for now.
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| Gold intends an EH attack on f6; Silver has prepared to blunt it. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
In the diagram at left, Gold has chosen a rather more aggressive setup. The elephant is placed to immediately attack the f6 trap in conjunction with a horse coming up the g-file. The camel, meanwhile, intends a secondary attack on the c6 trap, on the theory that the silver elephant will be tied up by the primary attack. The pressure exerted by the gold camel will make it difficult for Silver to keep a piece on b6, most particularly a horse.
Gold might as well start with several rabbits forward, too. Advanced rabbits are necessary to support an advanced camel, and they can increase the threat posed by an elephant-horse attack. Moreover, if Gold manages to share control of both c6 and f6, any advanced gold rabbits are in no immediate danger of capture.
Silver, in response, has allocated both elephant and camel to the defense of f6, hoping to take Gold's horse hostage if it advances. All of the silver rabbits are placed on the back row where they are not vulnerable to attack. Silver needn't fear that Gold will launch a lone-elphant attack up the middle to pull the d8 and e8 rabbits, because the vulnerability of Gold's camel insures Silver the upper hand in any rabbit-pulling opening. (Gold will have to voluntarily advance rabbits to keep the gold camel safe.) Silver supposes that Gold must attack given Gold's aggressive setup, so Silver is mostly concerned to make any EH attack on f6 costly for the invading horse.
Early Arimaa theory advocated placing all eight rabbits on the back row for both sides in every setup, but the average number of rabbits placed forward has been creeping upward as it becomes clear that advanced rabbits have positional value to offset their vulnerability to capture. As of October 2005, the initial setups on the Arimaa server averaged about one and a half rabbits in the front row.
Most players will split their horses, dogs, and cats to have one on each side of the board, in keeping with the principle that balanced forces are most effective. However, as top players experiment with setups including a decentralized elephant and/or decentralized camel, it seems occasionally advantageous to place both horses on the same wing, near the elephant and far from the camel.
