The rules of Chaturanga:
Note: This writeup only attempts to list the rules for one variant of Chaturanga. As the above writeup says no one is certain what the rules were.
Chaturanga, like International Chess has 32 pieces, 16 for each side and is played on a 64 square board. Unlike Xiangqi, the pieces are placed inside the squares (again like International Chess). The pieces are exactly the same as International Chess, except for the fact that the Bishop is known as the Elephant and the Queen as the Minister. The pieces move very similarly to International Chess:
King The King is like the International Chess King -- if he's checkmated, you lose. He moves just like the modern version, except that once in the game he is allowed to move as a Knight (i.e. one space in one direction and two along a perpendicular)
Minister The counselor can move one space in any diagonal direction.
Elephant Jumps over one square in the diagonal direction.
Horse Moves as in International Chess.
Infantryman (Pawn) As in International Chess, except that it does not have some capabilities that the Europeans gave to the pawn, i.e. two moves when starting and en passant (the origins of the two are related).
The neat thing about Chaturanga is that it can be played on a normal modern Chess board. There are, as mentioned above, other versions, some being played on a cross-shaped board and others using dice. (Indeed, the art of casting dice was practiced extensively in Ancient India -- it's said that some were so skilled that they could always control which face the dice would land on)