Accounting for symmetry, there are 32432400 possible setups for Gold, and twice as many for Silver. However, the setups of strong players almost always obey some simple rules:
- Elephant centralisation: the elephant usually starts on the d- or e-file; less commonly, on the c- or f-file.
- Activity: a stronger piece should not start behind a weaker piece.
- Defence: it should be possible to defend the key squares b3 and g3 (or b6 and g6) in the opening. Often this means putting a horse or camel on b2 and g2 (or b7 and g7).
- Balance: neither wing should be left vulnerable to attack.
- One should be cautious about setting up with many forward rabbits, as they might be pulled.
A small minority of the possible setups obey these rules. However, there is still plenty of scope for variation.
In the opening, the elephants tend to stay in the centre, while camels and horses often choose a wing. Therefore, the most basic characteristic of a setup is the positions of the camel and horses. A balanced setup (with the camel in the centre and a horse on each wing) is the most flexible; early in the history of Arimaa, these setups were popular with both colours. Around 2008 it became clear that unbalanced setups can be profitable for Silver. Balanced setups have remained very popular for Gold, due to a fear that Silver could respond to an unbalanced gold setup with a setup that gives Silver a favourable alignment. For instance, Silver will try to arrange that the silver camel is near the gold horses, while the silver horses are far from the gold camel.
The placement of cats and dogs is less significant and less easy to evaluate. Dogs are more likely to want to advance than cats, and are often placed in the centre for flexibility. Alternatively, dogs behind traps make the defence stronger. It is typical to split dogs and cats to have one on each wing, in keeping with the principle that balanced forces are most effective.
Early Arimaa theory advocated placing all eight rabbits on the back row for both sides in every setup, but it has become clear that advanced rabbits have positional value to offset their vulnerability to capture. For example, advanced rabbits can help support an advanced camel.
The diagram shows two standard balanced setups. Gold's setup, the 99of9, has been the most common gold setup since 2005. The other five setups differing only in cat and dog placement are also loosely known as 99of9 setups. The original idea behind the 99of9 was to protect Gold's rabbits by keeping them out of the centre. Rabbits on the d- and e-files can more easily be pulled by the opponent. Although generating a direct capture threat this way is very slow, they can get in the way of friendly pieces moving between the home traps. It also makes sense to place rabbits on the wings since it is usually easier to generate goal threats on the wings than in the centre.
Silver's setup, known as the Fritzlein setup, is perhaps slightly more inclined towards aggression. Although the c7 and f7 rabbits are fairly safe, playing a home game could be more awkward for Silver since the rabbits could be pulled into the traps, where they will get in Silver's way. Silver will therefore have to attack to justify her setup. The ability of the cats to advance, to occupy b6 and g6 or even support an attack, is a possible advantage of this setup.
Note that the silver elephant does not directly face the gold elephant. If it did, the gold elephant could immediately go to e6, which would be annoying for Silver. However, there are some unbalanced setups where it is safe for the silver elephant to face the gold elephant.
At left, Silver uses an unbalanced setup popularised by browni. Silver plans to move the elephant to d3, the horse to a3, and to bother the gold horse with her camel, aiming to quickly share control of the c3 trap. Gold will probably have to choose quickly whether to move his camel to the west for defence, or east for a counterattack against f6 with camel and horse. In the latter case the game will be sharp.
Experience has shown that the facing elephants are justified by Silver's attacking threat: if Gold tries to punish the silver setup with 2g Ed2nnnn, Silver will play 2s ha7s mb7s cc7w hg7s and 3s ed7wsse. Silver has lost some time with sideways steps, but the gold elephant is cut off from c3 where it will be needed for defence, so Gold must give the time back.
At right, Gold plays the browni setup. As above, the idea is get a quick attack in the west with elephant, camel and horse. Silver should not respond to this with a balanced setup, as the attacking threat in combination with the first move would give Gold a small but noticeable edge. Here Silver tries to take advantage of Gold's unbalanced setup by getting an alignment advantage. The silver camel will slow down Gold's attack; meanwhile, Silver is stronger than Gold in the east. Gold anticipates Silver's idea by putting a dog in the west. Depending on what the d7 horse does, Gold may be able to attack c6 with elephant, horse and dog, while moving the camel east to face the silver horses.
Another idea for Silver (illustrated here) would be to put the elephant in the west and camel and horse in the east, arguing that Silver will be faster in an attacking race since Silver's attack is further from the elephants. Yet another idea, from this game, is to play an approximate mirror image of Gold's setup, leading to a slow maneuvering opening.
Another type of unbalanced setup is shown at left. If Silver sets up with both horses on the same wing, Gold should usually respond by moving his camel to face them. Silver's idea is then to create a threat on that wing, restricting the gold elephant to defence, and use her camel as the strongest piece on the other wing. The threat is usually to pull a gold piece back to Silver's trap, and so this setup is typically played less aggressively than MH setups. If the gold horse is pulled, there are a range of horse framing tactics which are characteristic of this setup.
The proper response by Gold is an unsettled question. If the gold horse is able to advance in the west, this can lead to a strong attack on the c6 trap, but forcing the horse past the silver horses can be tricky. It may also be possible for Gold to attack the f6 trap with elephant and supporting pieces (usually horse and dog) since the f6 trap will be left very weak if the camel can be dislodged.
As with MH setups, HH setups are less popular for Gold. Silver can gain time by setting up with the camel already facing the gold horses. Silver might also avoid having a horse directly face the gold camel.
These statistics are based on games between two humans rated over 1800. Setups where one wing is left without either camel or horse are rare and excluded here. Note that in this classification, 'old-style' EHH setups (e.g. with b- and d-file horses) are counted as central horse setups.