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Unfortunately the exact rules of Petteia are not known (googling
for Petteia will give you interesting information about that game).

However, the soldier of Petteia may be the ancestor of the standard
chess pawn with its surprising divergent move and capture. 

You can find an interesting article by Myron Samsin on this theme 
on http://www.netcologne.de/~nc-jostenge/samsin.htm

--Jörg Knappen