Chaturanga is an ancient Indian game which is presumed to be the common ancestor of chess, xiangqi, shogi, janggi and makruk. It is the direct ancestor of shatranj which was the form that brought chess to medieval Europe. Each descendant has modified the ancient rules in a different way, but for simplicity only the differences with chess will be listed.
Bishops, which were called elephants, moved one square diagonally or one square forward (think of the four legs and trunk of the elephant). This is the one piece with a different move from Shatranj. This is the same move as the Silver general in Shogi.
The queen, which was called a vizier, moved exactly one square diagonally. This made it a rather weak piece.
Pawns in Chatrang did not have the option of moving two squares on the first move.
Pawns which reached the eighth rank were promoted, but only to a vizier.
Castling was not allowed.
Capturing the opponent's king was a win (There was no check or stalemate).
Capturing all one's opponent's pieces apart from the king (baring the king) was a win, unless your opponent could capture your last piece on their next move, when it is a draw.
The game was based on the fivefold divisions of the ancient Indian army:
Infantry represented by a line of advancing pawns
The King and his advisor or general in the center
Thundering elephants near the center of the army. As elephants fell from use the name of this piece went through several changes before became the Bishop in English.
Mounted cavalry represented by the horse with a move that facilitated flanking. This became the Knight with the distinctive move that marks a game as a likely descendant of Chaturanga.
Chariots on the wings which move quickly but linearly and became the Rook in Europe, but a ship as chess moved north into Russia.
